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 $49.92   12.181%   $56.0008   $56.00   $56.00   $56.00  
  Purchase #2 $243.38   11.573%   $271.5464   $271.55   $271.55   $271.50  
  Purchase #3 $184.87   6.727%   $197.3062   $197.31   $197.30   $197.30  
  Purchase #4 $67.37   5.299%   $70.9399   $70.94   $70.95   $70.90  
  Purchase #5 $156.94   7.690%   $169.0087   $169.01   $169.00   $169.00  
  Purchase #6 $203.89   12.192%   $228.7483   $228.75   $228.75   $228.70  
  Purchase #7 $61.27   13.370%   $69.4618   $69.46   $69.45   $69.50  
  7 purchase totals = $967.64       $1,063.0121   $1,063.02   $1,063.00   $1,062.90