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 $140.34   11.117%   $155.9416   $155.94   $155.95   $155.90  
  Purchase #2 $208.57   13.350%   $236.4141   $236.41   $236.40   $236.40  
  Purchase #3 $211.62   3.476%   $218.9759   $218.98   $219.00   $219.00  
  Purchase #4 $95.67   11.288%   $106.4692   $106.47   $106.45   $106.50  
  Purchase #5 $88.30   10.446%   $97.5238   $97.52   $97.50   $97.50  
  Purchase #6 $86.96   11.679%   $97.1161   $97.12   $97.10   $97.10  
  Purchase #7 $130.37   12.542%   $146.721   $146.72   $146.70   $146.70  
  7 purchase totals = $961.83       $1,059.1617   $1,059.16   $1,059.10   $1,059.10