Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $145.72   13.415%   $165.2683   $165.27   $165.25   $165.30  
  Purchase #2 $112.81   13.210%   $127.7122   $127.71   $127.70   $127.70  
  Purchase #3 $217.61   7.834%   $234.6576   $234.66   $234.65   $234.70  
  Purchase #4 $194.73   12.182%   $218.452   $218.45   $218.45   $218.50  
  Purchase #5 $119.92   4.563%   $125.3919   $125.39   $125.40   $125.40  
  Purchase #6 $110.70   11.596%   $123.5368   $123.54   $123.55   $123.50  
  Purchase #7 $108.68   6.102%   $115.3117   $115.31   $115.30   $115.30  
  7 purchase totals = $1,010.17       $1,110.3305   $1,110.33   $1,110.30   $1,110.40