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 $59.93   12.371%   $67.3439   $67.34   $67.35   $67.30  
  Purchase #2 $84.52   9.821%   $92.8207   $92.82   $92.80   $92.80  
  Purchase #3 $46.40   11.765%   $51.859   $51.86   $51.85   $51.90  
  Purchase #4 $223.53   10.455%   $246.9001   $246.90   $246.90   $246.90  
  Purchase #5 $233.51   7.460%   $250.9298   $250.93   $250.95   $250.90  
  Purchase #6 $202.71   10.209%   $223.4047   $223.40   $223.40   $223.40  
  Purchase #7 $136.88   6.185%   $145.346   $145.35   $145.35   $145.30  
  7 purchase totals = $987.48       $1,078.6042   $1,078.60   $1,078.60   $1,078.50