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 $86.54   6.293%   $91.986   $91.99   $92.00   $92.00  
  Purchase #2 $214.72   13.567%   $243.8511   $243.85   $243.85   $243.90  
  Purchase #3 $240.73   7.859%   $259.649   $259.65   $259.65   $259.60  
  Purchase #4 $195.92   5.772%   $207.2285   $207.23   $207.25   $207.20  
  Purchase #5 $158.81   13.832%   $180.7766   $180.78   $180.80   $180.80  
  Purchase #6 $204.39   6.801%   $218.2906   $218.29   $218.30   $218.30  
  Purchase #7 $39.73   9.638%   $43.5592   $43.56   $43.55   $43.60  
  7 purchase totals = $1,140.84       $1,245.3410   $1,245.35   $1,245.40   $1,245.40