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 $71.50   6.694%   $76.2862   $76.29   $76.30   $76.30  
  Purchase #2 $79.51   5.132%   $83.5905   $83.59   $83.60   $83.60  
  Purchase #3 $248.43   12.139%   $278.5869   $278.59   $278.60   $278.60  
  Purchase #4 $56.32   10.601%   $62.2905   $62.29   $62.30   $62.30  
  Purchase #5 $115.35   6.404%   $122.737   $122.74   $122.75   $122.70  
  Purchase #6 $185.49   4.706%   $194.2192   $194.22   $194.20   $194.20  
  Purchase #7 $131.41   9.218%   $143.5234   $143.52   $143.50   $143.50  
  7 purchase totals = $888.01       $961.2337   $961.24   $961.25   $961.20