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 $214.84   9.416%   $235.0693   $235.07   $235.05   $235.10  
  Purchase #2 $59.42   5.158%   $62.4849   $62.48   $62.50   $62.50  
  Purchase #3 $160.72   12.338%   $180.5496   $180.55   $180.55   $180.50  
  Purchase #4 $139.46   8.789%   $151.7171   $151.72   $151.70   $151.70  
  Purchase #5 $165.50   5.406%   $174.4469   $174.45   $174.45   $174.40  
  Purchase #6 $125.26   8.607%   $136.0411   $136.04   $136.05   $136.00  
  Purchase #7 $50.26   12.811%   $56.6988   $56.70   $56.70   $56.70  
  7 purchase totals = $915.46       $997.0077   $997.01   $997.00   $996.90