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 $56.35   13.339%   $63.8665   $63.87   $63.85   $63.90  
  Purchase #2 $188.27   4.736%   $197.1865   $197.19   $197.20   $197.20  
  Purchase #3 $152.80   10.586%   $168.9754   $168.98   $169.00   $169.00  
  Purchase #4 $217.40   13.138%   $245.962   $245.96   $245.95   $246.00  
  Purchase #5 $194.74   8.650%   $211.585   $211.59   $211.60   $211.60  
  Purchase #6 $97.65   13.556%   $110.8874   $110.89   $110.90   $110.90  
  Purchase #7 $140.92   3.648%   $146.0608   $146.06   $146.05   $146.10  
  7 purchase totals = $1,048.13       $1,144.5236   $1,144.54   $1,144.55   $1,144.70