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 $230.74   9.631%   $252.9626   $252.96   $252.95   $253.00  
  Purchase #2 $247.99   9.844%   $272.4021   $272.40   $272.40   $272.40  
  Purchase #3 $158.61   7.626%   $170.7056   $170.71   $170.70   $170.70  
  Purchase #4 $178.71   11.777%   $199.7567   $199.76   $199.75   $199.80  
  Purchase #5 $196.61   4.255%   $204.9758   $204.98   $205.00   $205.00  
  Purchase #6 $216.41   12.447%   $243.3466   $243.35   $243.35   $243.30  
  Purchase #7 $107.62   9.853%   $118.2238   $118.22   $118.20   $118.20  
  7 purchase totals = $1,336.69       $1,462.3732   $1,462.38   $1,462.35   $1,462.40