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 $153.98   9.342%   $168.3648   $168.36   $168.35   $168.40  
  Purchase #2 $240.93   10.449%   $266.1048   $266.10   $266.10   $266.10  
  Purchase #3 $226.33   12.715%   $255.1079   $255.11   $255.10   $255.10  
  Purchase #4 $87.79   3.432%   $90.803   $90.80   $90.80   $90.80  
  Purchase #5 $197.85   3.763%   $205.2951   $205.30   $205.30   $205.30  
  Purchase #6 $112.30   12.187%   $125.986   $125.99   $126.00   $126.00  
  Purchase #7 $217.58   11.581%   $242.7779   $242.78   $242.80   $242.80  
  7 purchase totals = $1,236.76       $1,354.4395   $1,354.44   $1,354.45   $1,354.50