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 $59.89   12.563%   $67.414   $67.41   $67.40   $67.40  
  Purchase #2 $73.78   7.449%   $79.2759   $79.28   $79.30   $79.30  
  Purchase #3 $227.57   9.741%   $249.7376   $249.74   $249.75   $249.70  
  Purchase #4 $108.47   13.697%   $123.3271   $123.33   $123.35   $123.30  
  Purchase #5 $208.50   11.643%   $232.7757   $232.78   $232.80   $232.80  
  Purchase #6 $196.78   5.299%   $207.2074   $207.21   $207.20   $207.20  
  Purchase #7 $55.60   13.172%   $62.9236   $62.92   $62.90   $62.90  
  7 purchase totals = $930.59       $1,022.6613   $1,022.67   $1,022.70   $1,022.60