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 $59.57   5.646%   $62.9333   $62.93   $62.95   $62.90  
  Purchase #2 $214.31   11.303%   $238.5335   $238.53   $238.55   $238.50  
  Purchase #3 $167.78   5.815%   $177.5364   $177.54   $177.55   $177.50  
  Purchase #4 $29.56   8.482%   $32.0673   $32.07   $32.05   $32.10  
  Purchase #5 $142.94   4.293%   $149.0764   $149.08   $149.10   $149.10  
  Purchase #6 $121.72   8.777%   $132.4034   $132.40   $132.40   $132.40  
  Purchase #7 $11.80   6.753%   $12.5969   $12.60   $12.60   $12.60  
  7 purchase totals = $747.68       $805.1472   $805.15   $805.20   $805.10