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 $67.35   11.103%   $74.8279   $74.83   $74.85   $74.80  
  Purchase #2 $84.68   9.168%   $92.4435   $92.44   $92.45   $92.40  
  Purchase #3 $243.89   9.549%   $267.1791   $267.18   $267.20   $267.20  
  Purchase #4 $192.75   4.744%   $201.8941   $201.89   $201.90   $201.90  
  Purchase #5 $231.80   12.331%   $260.3833   $260.38   $260.40   $260.40  
  Purchase #6 $58.91   10.263%   $64.9559   $64.96   $64.95   $65.00  
  Purchase #7 $92.49   10.510%   $102.2107   $102.21   $102.20   $102.20  
  7 purchase totals = $971.87       $1,063.8945   $1,063.89   $1,063.95   $1,063.90