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 $192.80   6.148%   $204.6533   $204.65   $204.65   $204.70  
  Purchase #2 $213.46   3.508%   $220.9482   $220.95   $220.95   $220.90  
  Purchase #3 $207.88   6.599%   $221.598   $221.60   $221.60   $221.60  
  Purchase #4 $51.61   6.431%   $54.929   $54.93   $54.95   $54.90  
  Purchase #5 $57.37   10.858%   $63.5992   $63.60   $63.60   $63.60  
  Purchase #6 $68.69   13.862%   $78.2118   $78.21   $78.20   $78.20  
  Purchase #7 $184.79   11.738%   $206.4807   $206.48   $206.50   $206.50  
  7 purchase totals = $976.60       $1,050.4202   $1,050.42   $1,050.45   $1,050.40