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 $204.68   12.211%   $229.6735   $229.67   $229.65   $229.70  
  Purchase #2 $214.63   11.489%   $239.2888   $239.29   $239.30   $239.30  
  Purchase #3 $76.69   7.274%   $82.2684   $82.27   $82.25   $82.30  
  Purchase #4 $181.25   11.644%   $202.3548   $202.35   $202.35   $202.40  
  Purchase #5 $243.72   12.771%   $274.8455   $274.85   $274.85   $274.80  
  Purchase #6 $135.84   6.269%   $144.3558   $144.36   $144.35   $144.40  
  Purchase #7 $183.96   5.130%   $193.3971   $193.40   $193.40   $193.40  
  7 purchase totals = $1,240.77       $1,366.1839   $1,366.19   $1,366.15   $1,366.30