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 $249.86   9.720%   $274.1464   $274.15   $274.15   $274.10  
  Purchase #2 $245.85   5.741%   $259.9642   $259.96   $259.95   $260.00  
  Purchase #3 $197.27   11.789%   $220.5262   $220.53   $220.55   $220.50  
  Purchase #4 $221.93   5.446%   $234.0163   $234.02   $234.00   $234.00  
  Purchase #5 $61.85   5.346%   $65.1565   $65.16   $65.15   $65.20  
  Purchase #6 $170.98   11.169%   $190.0768   $190.08   $190.10   $190.10  
  Purchase #7 $207.49   8.172%   $224.4461   $224.45   $224.45   $224.40  
  7 purchase totals = $1,355.23       $1,468.3325   $1,468.35   $1,468.35   $1,468.30