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 $73.86   3.753%   $76.632   $76.63   $76.65   $76.60  
  Purchase #2 $112.56   6.188%   $119.5252   $119.53   $119.55   $119.50  
  Purchase #3 $6.30   10.442%   $6.9578   $6.96   $6.95   $7.00  
  Purchase #4 $202.50   6.117%   $214.8869   $214.89   $214.90   $214.90  
  Purchase #5 $58.67   6.369%   $62.4067   $62.41   $62.40   $62.40  
  Purchase #6 $204.78   3.594%   $212.1398   $212.14   $212.15   $212.10  
  Purchase #7 $87.84   8.787%   $95.5585   $95.56   $95.55   $95.60  
  7 purchase totals = $746.51       $788.1069   $788.12   $788.15   $788.10