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 $190.95   8.741%   $207.6409   $207.64   $207.65   $207.60  
  Purchase #2 $138.29   11.573%   $154.2943   $154.29   $154.30   $154.30  
  Purchase #3 $87.90   9.496%   $96.247   $96.25   $96.25   $96.20  
  Purchase #4 $216.71   11.612%   $241.8744   $241.87   $241.85   $241.90  
  Purchase #5 $216.41   13.311%   $245.2163   $245.22   $245.20   $245.20  
  Purchase #6 $244.65   4.435%   $255.5002   $255.50   $255.50   $255.50  
  Purchase #7 $171.30   13.299%   $194.0812   $194.08   $194.10   $194.10  
  7 purchase totals = $1,266.21       $1,394.8543   $1,394.85   $1,394.85   $1,394.80