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 $232.57   13.517%   $264.0065   $264.01   $264.00   $264.00  
  Purchase #2 $62.64   9.431%   $68.5476   $68.55   $68.55   $68.50  
  Purchase #3 $195.78   4.825%   $205.2264   $205.23   $205.25   $205.20  
  Purchase #4 $214.55   8.304%   $232.3662   $232.37   $232.35   $232.40  
  Purchase #5 $125.38   7.840%   $135.2098   $135.21   $135.20   $135.20  
  Purchase #6 $147.31   7.825%   $158.837   $158.84   $158.85   $158.80  
  Purchase #7 $163.38   13.303%   $185.1144   $185.11   $185.10   $185.10  
  7 purchase totals = $1,141.61       $1,249.3079   $1,249.32   $1,249.30   $1,249.20