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 $136.33   11.588%   $152.1279   $152.13   $152.15   $152.10  
  Purchase #2 $62.96   3.379%   $65.0874   $65.09   $65.10   $65.10  
  Purchase #3 $222.56   11.440%   $248.0209   $248.02   $248.00   $248.00  
  Purchase #4 $151.85   10.480%   $167.7639   $167.76   $167.75   $167.80  
  Purchase #5 $231.64   12.843%   $261.3895   $261.39   $261.40   $261.40  
  Purchase #6 $146.54   11.363%   $163.1913   $163.19   $163.20   $163.20  
  Purchase #7 $41.57   12.841%   $46.908   $46.91   $46.90   $46.90  
  7 purchase totals = $993.45       $1,104.4889   $1,104.49   $1,104.50   $1,104.50