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 $60.66   7.777%   $65.3775   $65.38   $65.40   $65.40  
  Purchase #2 $173.85   4.336%   $181.3881   $181.39   $181.40   $181.40  
  Purchase #3 $23.43   6.604%   $24.9773   $24.98   $25.00   $25.00  
  Purchase #4 $219.63   3.316%   $226.9129   $226.91   $226.90   $226.90  
  Purchase #5 $119.60   8.531%   $129.8031   $129.80   $129.80   $129.80  
  Purchase #6 $205.53   5.162%   $216.1395   $216.14   $216.15   $216.10  
  Purchase #7 $125.68   12.166%   $140.9702   $140.97   $140.95   $141.00  
  7 purchase totals = $928.38       $985.5686   $985.57   $985.60   $985.60