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 $32.26   11.526%   $35.9783   $35.98   $36.00   $36.00  
  Purchase #2 $90.85   7.385%   $97.5593   $97.56   $97.55   $97.60  
  Purchase #3 $33.57   3.618%   $34.7846   $34.78   $34.80   $34.80  
  Purchase #4 $221.52   7.170%   $237.403   $237.40   $237.40   $237.40  
  Purchase #5 $92.65   4.662%   $96.9693   $96.97   $96.95   $97.00  
  Purchase #6 $77.61   13.543%   $88.1207   $88.12   $88.10   $88.10  
  Purchase #7 $130.92   12.128%   $146.798   $146.80   $146.80   $146.80  
  7 purchase totals = $679.38       $737.6132   $737.61   $737.60   $737.70