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 $49.99   9.554%   $54.766   $54.77   $54.75   $54.80  
  Purchase #2 $92.51   4.686%   $96.845   $96.85   $96.85   $96.80  
  Purchase #3 $164.41   12.387%   $184.7755   $184.78   $184.80   $184.80  
  Purchase #4 $205.58   12.163%   $230.5847   $230.58   $230.60   $230.60  
  Purchase #5 $92.73   10.702%   $102.654   $102.65   $102.65   $102.70  
  Purchase #6 $137.63   13.662%   $156.433   $156.43   $156.45   $156.40  
  Purchase #7 $203.86   6.399%   $216.905   $216.91   $216.90   $216.90  
  7 purchase totals = $946.71       $1,042.9632   $1,042.97   $1,043.00   $1,043.00