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 $76.99   7.386%   $82.6765   $82.68   $82.70   $82.70  
  Purchase #2 $242.70   12.753%   $273.6515   $273.65   $273.65   $273.70  
  Purchase #3 $48.71   9.365%   $53.2717   $53.27   $53.25   $53.30  
  Purchase #4 $144.95   9.692%   $158.9986   $159.00   $159.00   $159.00  
  Purchase #5 $17.37   11.592%   $19.3835   $19.38   $19.40   $19.40  
  Purchase #6 $189.78   11.685%   $211.9558   $211.96   $211.95   $212.00  
  Purchase #7 $116.46   8.645%   $126.528   $126.53   $126.55   $126.50  
  7 purchase totals = $836.96       $926.4656   $926.47   $926.50   $926.60