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 $160.85   11.290%   $179.01   $179.01   $179.00   $179.00  
  Purchase #2 $148.33   3.691%   $153.8049   $153.80   $153.80   $153.80  
  Purchase #3 $9.48   8.190%   $10.2564   $10.26   $10.25   $10.30  
  Purchase #4 $116.89   7.577%   $125.7468   $125.75   $125.75   $125.70  
  Purchase #5 $55.80   9.327%   $61.0045   $61.00   $61.00   $61.00  
  Purchase #6 $224.51   5.117%   $235.9982   $236.00   $236.00   $236.00  
  Purchase #7 $14.90   10.553%   $16.4724   $16.47   $16.45   $16.50  
  7 purchase totals = $730.76       $782.2932   $782.29   $782.25   $782.30