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 $62.90   5.823%   $66.5627   $66.56   $66.55   $66.60  
  Purchase #2 $180.65   9.354%   $197.548   $197.55   $197.55   $197.50  
  Purchase #3 $11.62   11.690%   $12.9784   $12.98   $13.00   $13.00  
  Purchase #4 $245.37   4.573%   $256.5908   $256.59   $256.60   $256.60  
  Purchase #5 $51.58   11.750%   $57.6407   $57.64   $57.65   $57.60  
  Purchase #6 $160.43   12.642%   $180.7116   $180.71   $180.70   $180.70  
  Purchase #7 $119.65   10.151%   $131.7957   $131.80   $131.80   $131.80  
  7 purchase totals = $832.20       $903.8279   $903.83   $903.85   $903.80