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 $86.41   13.226%   $97.8386   $97.84   $97.85   $97.80  
  Purchase #2 $213.55   11.215%   $237.4996   $237.50   $237.50   $237.50  
  Purchase #3 $173.88   8.118%   $187.9956   $188.00   $188.00   $188.00  
  Purchase #4 $195.88   10.641%   $216.7236   $216.72   $216.70   $216.70  
  Purchase #5 $238.28   10.667%   $263.6973   $263.70   $263.70   $263.70  
  Purchase #6 $239.62   11.802%   $267.9   $267.90   $267.90   $267.90  
  Purchase #7 $145.46   6.441%   $154.8291   $154.83   $154.85   $154.80  
  7 purchase totals = $1,293.08       $1,426.4838   $1,426.49   $1,426.50   $1,426.40