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 $168.57   9.758%   $185.0191   $185.02   $185.00   $185.00  
  Purchase #2 $116.74   3.517%   $120.8457   $120.85   $120.85   $120.80  
  Purchase #3 $108.32   7.262%   $116.1862   $116.19   $116.20   $116.20  
  Purchase #4 $60.94   3.664%   $63.1728   $63.17   $63.15   $63.20  
  Purchase #5 $186.43   10.244%   $205.5279   $205.53   $205.55   $205.50  
  Purchase #6 $193.97   10.161%   $213.6793   $213.68   $213.70   $213.70  
  Purchase #7 $133.74   7.742%   $144.0942   $144.09   $144.10   $144.10  
  7 purchase totals = $968.71       $1,048.5252   $1,048.53   $1,048.55   $1,048.50