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 $234.55   11.842%   $262.3254   $262.33   $262.35   $262.30  
  Purchase #2 $166.63   6.157%   $176.8894   $176.89   $176.90   $176.90  
  Purchase #3 $109.71   3.202%   $113.2229   $113.22   $113.20   $113.20  
  Purchase #4 $96.53   12.319%   $108.4215   $108.42   $108.40   $108.40  
  Purchase #5 $240.91   8.256%   $260.7995   $260.80   $260.80   $260.80  
  Purchase #6 $189.72   12.298%   $213.0518   $213.05   $213.05   $213.10  
  Purchase #7 $31.47   8.698%   $34.2073   $34.21   $34.20   $34.20  
  7 purchase totals = $1,069.52       $1,168.9178   $1,168.92   $1,168.90   $1,168.90