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 $195.27   6.829%   $208.605   $208.61   $208.60   $208.60  
  Purchase #2 $33.67   10.433%   $37.1828   $37.18   $37.20   $37.20  
  Purchase #3 $235.91   11.771%   $263.679   $263.68   $263.70   $263.70  
  Purchase #4 $14.70   12.611%   $16.5538   $16.55   $16.55   $16.60  
  Purchase #5 $32.26   3.847%   $33.501   $33.50   $33.50   $33.50  
  Purchase #6 $9.74   10.628%   $10.7752   $10.78   $10.80   $10.80  
  Purchase #7 $25.55   8.404%   $27.6972   $27.70   $27.70   $27.70  
  7 purchase totals = $547.10       $597.9940   $598.00   $598.05   $598.10