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 $157.93   11.788%   $176.5468   $176.55   $176.55   $176.50  
  Purchase #2 $59.91   13.245%   $67.8451   $67.85   $67.85   $67.80  
  Purchase #3 $172.78   6.815%   $184.555   $184.56   $184.55   $184.60  
  Purchase #4 $238.65   11.192%   $265.3597   $265.36   $265.35   $265.40  
  Purchase #5 $239.97   3.810%   $249.1129   $249.11   $249.10   $249.10  
  Purchase #6 $134.34   8.475%   $145.7253   $145.73   $145.75   $145.70  
  Purchase #7 $152.86   3.834%   $158.7207   $158.72   $158.70   $158.70  
  7 purchase totals = $1,156.44       $1,247.8655   $1,247.88   $1,247.85   $1,247.80