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 $62.66   3.207%   $64.6695   $64.67   $64.65   $64.70  
  Purchase #2 $162.59   12.669%   $183.1885   $183.19   $183.20   $183.20  
  Purchase #3 $94.30   10.822%   $104.5051   $104.51   $104.50   $104.50  
  Purchase #4 $52.35   9.779%   $57.4693   $57.47   $57.45   $57.50  
  Purchase #5 $171.67   10.772%   $190.1623   $190.16   $190.15   $190.20  
  Purchase #6 $221.87   4.493%   $231.8386   $231.84   $231.85   $231.80  
  Purchase #7 $12.34   6.707%   $13.1676   $13.17   $13.15   $13.20  
  7 purchase totals = $777.78       $845.0009   $845.01   $844.95   $845.10