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 $208.43   8.793%   $226.7572   $226.76   $226.75   $226.80  
  Purchase #2 $88.78   9.232%   $96.9762   $96.98   $97.00   $97.00  
  Purchase #3 $238.35   7.717%   $256.7435   $256.74   $256.75   $256.70  
  Purchase #4 $54.88   12.811%   $61.9107   $61.91   $61.90   $61.90  
  Purchase #5 $175.90   12.694%   $198.2287   $198.23   $198.25   $198.20  
  Purchase #6 $223.99   8.220%   $242.402   $242.40   $242.40   $242.40  
  Purchase #7 $154.49   6.317%   $164.2491   $164.25   $164.25   $164.20  
  7 purchase totals = $1,144.82       $1,247.2674   $1,247.27   $1,247.30   $1,247.20