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 $73.74   4.113%   $76.7729   $76.77   $76.75   $76.80  
  Purchase #2 $131.82   9.793%   $144.7291   $144.73   $144.75   $144.70  
  Purchase #3 $73.99   13.526%   $83.9979   $84.00   $84.00   $84.00  
  Purchase #4 $232.79   4.781%   $243.9197   $243.92   $243.90   $243.90  
  Purchase #5 $112.65   6.117%   $119.5408   $119.54   $119.55   $119.50  
  Purchase #6 $230.69   9.385%   $252.3403   $252.34   $252.35   $252.30  
  Purchase #7 $200.46   5.862%   $212.211   $212.21   $212.20   $212.20  
  7 purchase totals = $1,056.14       $1,133.5117   $1,133.51   $1,133.50   $1,133.40