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 $158.53   3.753%   $164.4796   $164.48   $164.50   $164.50  
  Purchase #2 $235.33   11.323%   $261.9764   $261.98   $262.00   $262.00  
  Purchase #3 $221.25   5.716%   $233.8967   $233.90   $233.90   $233.90  
  Purchase #4 $112.71   12.376%   $126.659   $126.66   $126.65   $126.70  
  Purchase #5 $86.93   3.701%   $90.1473   $90.15   $90.15   $90.10  
  Purchase #6 $177.41   4.708%   $185.7625   $185.76   $185.75   $185.80  
  Purchase #7 $191.98   6.251%   $203.9807   $203.98   $204.00   $204.00  
  7 purchase totals = $1,184.14       $1,266.9022   $1,266.91   $1,266.95   $1,267.00