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 $110.71   12.224%   $124.2432   $124.24   $124.25   $124.20  
  Purchase #2 $208.87   11.149%   $232.1569   $232.16   $232.15   $232.20  
  Purchase #3 $151.96   4.198%   $158.3393   $158.34   $158.35   $158.30  
  Purchase #4 $206.32   9.284%   $225.4747   $225.47   $225.45   $225.50  
  Purchase #5 $189.87   8.401%   $205.821   $205.82   $205.80   $205.80  
  Purchase #6 $241.66   13.270%   $273.7283   $273.73   $273.75   $273.70  
  Purchase #7 $26.80   5.159%   $28.1826   $28.18   $28.20   $28.20  
  7 purchase totals = $1,136.19       $1,247.9460   $1,247.94   $1,247.95   $1,247.90