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 $151.89   8.308%   $164.509   $164.51   $164.50   $164.50  
  Purchase #2 $118.84   8.508%   $128.9509   $128.95   $128.95   $129.00  
  Purchase #3 $8.40   7.285%   $9.0119   $9.01   $9.00   $9.00  
  Purchase #4 $64.29   10.126%   $70.8   $70.80   $70.80   $70.80  
  Purchase #5 $35.86   10.714%   $39.702   $39.70   $39.70   $39.70  
  Purchase #6 $234.49   5.504%   $247.3963   $247.40   $247.40   $247.40  
  Purchase #7 $76.28   8.624%   $82.8584   $82.86   $82.85   $82.90  
  7 purchase totals = $690.05       $743.2285   $743.23   $743.20   $743.30