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 $23.76   13.323%   $26.9255   $26.93   $26.95   $26.90  
  Purchase #2 $230.35   7.543%   $247.7253   $247.73   $247.75   $247.70  
  Purchase #3 $24.68   11.738%   $27.5769   $27.58   $27.60   $27.60  
  Purchase #4 $196.94   10.159%   $216.9471   $216.95   $216.95   $216.90  
  Purchase #5 $229.29   4.609%   $239.858   $239.86   $239.85   $239.90  
  Purchase #6 $131.52   13.761%   $149.6185   $149.62   $149.60   $149.60  
  Purchase #7 $34.29   9.550%   $37.5647   $37.56   $37.55   $37.60  
  7 purchase totals = $870.83       $946.2160   $946.23   $946.25   $946.20