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 $246.51   8.361%   $267.1207   $267.12   $267.10   $267.10  
  Purchase #2 $154.78   13.830%   $176.1861   $176.19   $176.20   $176.20  
  Purchase #3 $189.83   3.357%   $196.2026   $196.20   $196.20   $196.20  
  Purchase #4 $195.28   4.450%   $203.97   $203.97   $203.95   $204.00  
  Purchase #5 $102.73   4.485%   $107.3374   $107.34   $107.35   $107.30  
  Purchase #6 $217.77   10.730%   $241.1367   $241.14   $241.15   $241.10  
  Purchase #7 $120.46   13.315%   $136.4992   $136.50   $136.50   $136.50  
  7 purchase totals = $1,227.36       $1,328.4527   $1,328.46   $1,328.45   $1,328.40