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 $104.92   4.219%   $109.3466   $109.35   $109.35   $109.30  
  Purchase #2 $162.78   12.596%   $183.2838   $183.28   $183.30   $183.30  
  Purchase #3 $117.75   11.706%   $131.5338   $131.53   $131.55   $131.50  
  Purchase #4 $216.30   5.139%   $227.4157   $227.42   $227.40   $227.40  
  Purchase #5 $192.49   9.126%   $210.0566   $210.06   $210.05   $210.10  
  Purchase #6 $205.96   6.588%   $219.5286   $219.53   $219.55   $219.50  
  Purchase #7 $196.26   4.451%   $204.9955   $205.00   $205.00   $205.00  
  7 purchase totals = $1,196.46       $1,286.1606   $1,286.17   $1,286.20   $1,286.10