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 $104.27   12.400%   $117.1995   $117.20   $117.20   $117.20  
  Purchase #2 $167.63   7.756%   $180.6314   $180.63   $180.65   $180.60  
  Purchase #3 $32.73   6.295%   $34.7904   $34.79   $34.80   $34.80  
  Purchase #4 $149.94   12.326%   $168.4216   $168.42   $168.40   $168.40  
  Purchase #5 $156.55   12.120%   $175.5239   $175.52   $175.50   $175.50  
  Purchase #6 $164.51   13.774%   $187.1696   $187.17   $187.15   $187.20  
  Purchase #7 $197.27   5.197%   $207.5221   $207.52   $207.50   $207.50  
  7 purchase totals = $972.90       $1,071.2585   $1,071.25   $1,071.20   $1,071.20