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 $84.31   12.771%   $95.0772   $95.08   $95.10   $95.10  
  Purchase #2 $208.37   4.499%   $217.7446   $217.74   $217.75   $217.70  
  Purchase #3 $114.30   10.342%   $126.1209   $126.12   $126.10   $126.10  
  Purchase #4 $162.73   13.346%   $184.4479   $184.45   $184.45   $184.40  
  Purchase #5 $38.48   7.219%   $41.2579   $41.26   $41.25   $41.30  
  Purchase #6 $246.52   13.835%   $280.626   $280.63   $280.65   $280.60  
  Purchase #7 $16.72   7.612%   $17.9927   $17.99   $18.00   $18.00  
  7 purchase totals = $871.43       $963.2672   $963.27   $963.30   $963.20