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 $239.91   5.142%   $252.2462   $252.25   $252.25   $252.20  
  Purchase #2 $223.77   3.107%   $230.7225   $230.72   $230.70   $230.70  
  Purchase #3 $70.43   5.494%   $74.2994   $74.30   $74.30   $74.30  
  Purchase #4 $226.95   8.593%   $246.4518   $246.45   $246.45   $246.50  
  Purchase #5 $43.34   10.792%   $48.0173   $48.02   $48.00   $48.00  
  Purchase #6 $179.49   5.844%   $189.9794   $189.98   $190.00   $190.00  
  Purchase #7 $204.83   4.536%   $214.1211   $214.12   $214.10   $214.10  
  7 purchase totals = $1,188.72       $1,255.8377   $1,255.84   $1,255.80   $1,255.80