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 $21.92   9.708%   $24.048   $24.05   $24.05   $24.00  
  Purchase #2 $124.31   11.474%   $138.5733   $138.57   $138.55   $138.60  
  Purchase #3 $162.91   8.699%   $177.0815   $177.08   $177.10   $177.10  
  Purchase #4 $247.87   8.115%   $267.9847   $267.98   $268.00   $268.00  
  Purchase #5 $84.49   3.681%   $87.6001   $87.60   $87.60   $87.60  
  Purchase #6 $143.41   4.780%   $150.265   $150.27   $150.25   $150.30  
  Purchase #7 $18.49   3.111%   $19.0652   $19.07   $19.05   $19.10  
  7 purchase totals = $803.40       $864.6178   $864.62   $864.60   $864.70