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 $187.66   7.759%   $202.2205   $202.22   $202.20   $202.20  
  Purchase #2 $247.65   10.246%   $273.0242   $273.02   $273.00   $273.00  
  Purchase #3 $125.81   6.722%   $134.2669   $134.27   $134.25   $134.30  
  Purchase #4 $57.68   5.581%   $60.8991   $60.90   $60.90   $60.90  
  Purchase #5 $64.81   4.508%   $67.7316   $67.73   $67.75   $67.70  
  Purchase #6 $109.75   4.636%   $114.838   $114.84   $114.85   $114.80  
  Purchase #7 $139.61   7.299%   $149.8001   $149.80   $149.80   $149.80  
  7 purchase totals = $932.97       $1,002.7804   $1,002.78   $1,002.75   $1,002.70