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 $216.63   8.321%   $234.6558   $234.66   $234.65   $234.70  
  Purchase #2 $109.90   5.371%   $115.8027   $115.80   $115.80   $115.80  
  Purchase #3 $99.32   9.637%   $108.8915   $108.89   $108.90   $108.90  
  Purchase #4 $200.30   11.836%   $224.0075   $224.01   $224.00   $224.00  
  Purchase #5 $195.90   8.535%   $212.6201   $212.62   $212.60   $212.60  
  Purchase #6 $247.47   7.327%   $265.6021   $265.60   $265.60   $265.60  
  Purchase #7 $82.63   13.695%   $93.9462   $93.95   $93.95   $93.90  
  7 purchase totals = $1,152.15       $1,255.5259   $1,255.53   $1,255.50   $1,255.50