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 $66.32   13.106%   $75.0119   $75.01   $75.00   $75.00  
  Purchase #2 $118.94   11.280%   $132.3564   $132.36   $132.35   $132.40  
  Purchase #3 $203.80   13.367%   $231.0419   $231.04   $231.05   $231.00  
  Purchase #4 $49.84   10.244%   $54.9456   $54.95   $54.95   $54.90  
  Purchase #5 $119.86   10.176%   $132.057   $132.06   $132.05   $132.10  
  Purchase #6 $29.71   10.567%   $32.8495   $32.85   $32.85   $32.80  
  Purchase #7 $171.77   8.263%   $185.9634   $185.96   $185.95   $186.00  
  7 purchase totals = $760.24       $844.2257   $844.23   $844.20   $844.20