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 $122.48   11.607%   $136.6963   $136.70   $136.70   $136.70  
  Purchase #2 $211.81   13.144%   $239.6503   $239.65   $239.65   $239.70  
  Purchase #3 $110.68   8.394%   $119.9705   $119.97   $119.95   $120.00  
  Purchase #4 $153.51   7.520%   $165.054   $165.05   $165.05   $165.10  
  Purchase #5 $75.37   13.235%   $85.3452   $85.35   $85.35   $85.30  
  Purchase #6 $222.63   12.581%   $250.6391   $250.64   $250.65   $250.60  
  Purchase #7 $61.70   4.474%   $64.4605   $64.46   $64.45   $64.50  
  7 purchase totals = $958.18       $1,061.8159   $1,061.82   $1,061.80   $1,061.90