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 $64.33   3.731%   $66.7302   $66.73   $66.75   $66.70  
  Purchase #2 $236.99   6.734%   $252.9489   $252.95   $252.95   $252.90  
  Purchase #3 $54.60   7.198%   $58.5301   $58.53   $58.55   $58.50  
  Purchase #4 $85.34   13.672%   $97.0077   $97.01   $97.00   $97.00  
  Purchase #5 $131.62   8.864%   $143.2868   $143.29   $143.30   $143.30  
  Purchase #6 $214.63   13.818%   $244.2876   $244.29   $244.30   $244.30  
  Purchase #7 $190.51   7.432%   $204.6687   $204.67   $204.65   $204.70  
  7 purchase totals = $978.02       $1,067.4600   $1,067.47   $1,067.50   $1,067.40