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 $249.81   10.160%   $275.1907   $275.19   $275.20   $275.20  
  Purchase #2 $93.83   3.857%   $97.449   $97.45   $97.45   $97.40  
  Purchase #3 $109.79   5.547%   $115.8801   $115.88   $115.90   $115.90  
  Purchase #4 $44.43   8.322%   $48.1275   $48.13   $48.15   $48.10  
  Purchase #5 $26.95   9.494%   $29.5086   $29.51   $29.50   $29.50  
  Purchase #6 $233.70   8.863%   $254.4128   $254.41   $254.40   $254.40  
  Purchase #7 $175.29   6.140%   $186.0528   $186.05   $186.05   $186.10  
  7 purchase totals = $933.80       $1,006.6215   $1,006.62   $1,006.65   $1,006.60