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 $186.82   9.585%   $204.7267   $204.73   $204.75   $204.70  
  Purchase #2 $108.37   4.130%   $112.8457   $112.85   $112.85   $112.80  
  Purchase #3 $206.55   4.575%   $215.9997   $216.00   $216.00   $216.00  
  Purchase #4 $60.50   9.692%   $66.3637   $66.36   $66.35   $66.40  
  Purchase #5 $243.68   9.683%   $267.2755   $267.28   $267.30   $267.30  
  Purchase #6 $47.40   5.307%   $49.9155   $49.92   $49.90   $49.90  
  Purchase #7 $100.61   7.264%   $107.9183   $107.92   $107.90   $107.90  
  7 purchase totals = $953.93       $1,025.0451   $1,025.06   $1,025.05   $1,025.00