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 $28.90   13.595%   $32.829   $32.83   $32.85   $32.80  
  Purchase #2 $144.52   3.405%   $149.4409   $149.44   $149.45   $149.40  
  Purchase #3 $156.97   3.495%   $162.4561   $162.46   $162.45   $162.50  
  Purchase #4 $223.83   5.344%   $235.7915   $235.79   $235.80   $235.80  
  Purchase #5 $232.50   6.600%   $247.845   $247.85   $247.85   $247.80  
  Purchase #6 $61.88   9.541%   $67.784   $67.78   $67.80   $67.80  
  Purchase #7 $242.27   9.347%   $264.915   $264.92   $264.90   $264.90  
  7 purchase totals = $1,090.87       $1,161.0615   $1,161.07   $1,161.10   $1,161.00