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 $188.79   11.790%   $211.0483   $211.05   $211.05   $211.00  
  Purchase #2 $99.28   9.390%   $108.6024   $108.60   $108.60   $108.60  
  Purchase #3 $211.94   4.484%   $221.4434   $221.44   $221.45   $221.40  
  Purchase #4 $44.88   13.184%   $50.797   $50.80   $50.80   $50.80  
  Purchase #5 $162.83   8.561%   $176.7699   $176.77   $176.75   $176.80  
  Purchase #6 $247.63   4.549%   $258.8947   $258.89   $258.90   $258.90  
  Purchase #7 $76.96   7.146%   $82.4596   $82.46   $82.45   $82.50  
  7 purchase totals = $1,032.31       $1,110.0153   $1,110.01   $1,110.00   $1,110.00