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 $55.54   11.635%   $62.0021   $62.00   $62.00   $62.00  
  Purchase #2 $76.65   8.603%   $83.2442   $83.24   $83.25   $83.20  
  Purchase #3 $39.98   6.693%   $42.6559   $42.66   $42.65   $42.70  
  Purchase #4 $171.71   4.735%   $179.8405   $179.84   $179.85   $179.80  
  Purchase #5 $120.89   9.161%   $131.9647   $131.96   $131.95   $132.00  
  Purchase #6 $194.29   6.848%   $207.595   $207.60   $207.60   $207.60  
  Purchase #7 $91.29   4.599%   $95.4884   $95.49   $95.50   $95.50  
  7 purchase totals = $750.35       $802.7908   $802.79   $802.80   $802.80