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 $184.45   6.658%   $196.7307   $196.73   $196.75   $196.70  
  Purchase #2 $73.98   13.432%   $83.917   $83.92   $83.90   $83.90  
  Purchase #3 $66.40   13.178%   $75.1502   $75.15   $75.15   $75.20  
  Purchase #4 $182.91   12.526%   $205.8213   $205.82   $205.80   $205.80  
  Purchase #5 $107.83   12.732%   $121.5589   $121.56   $121.55   $121.60  
  Purchase #6 $196.80   3.149%   $202.9972   $203.00   $203.00   $203.00  
  Purchase #7 $197.30   13.802%   $224.5313   $224.53   $224.55   $224.50  
  7 purchase totals = $1,009.67       $1,110.7066   $1,110.71   $1,110.70   $1,110.70