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 $176.97   12.453%   $199.0081   $199.01   $199.00   $199.00  
  Purchase #2 $24.97   3.484%   $25.84   $25.84   $25.85   $25.80  
  Purchase #3 $159.55   8.427%   $172.9953   $173.00   $173.00   $173.00  
  Purchase #4 $185.98   7.766%   $200.4232   $200.42   $200.40   $200.40  
  Purchase #5 $165.93   13.306%   $188.0086   $188.01   $188.00   $188.00  
  Purchase #6 $212.34   11.694%   $237.171   $237.17   $237.15   $237.20  
  Purchase #7 $55.62   13.392%   $63.0686   $63.07   $63.05   $63.10  
  7 purchase totals = $981.36       $1,086.5148   $1,086.52   $1,086.45   $1,086.50