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 $242.41   10.518%   $267.9067   $267.91   $267.90   $267.90  
  Purchase #2 $82.30   13.488%   $93.4006   $93.40   $93.40   $93.40  
  Purchase #3 $194.33   12.580%   $218.7767   $218.78   $218.80   $218.80  
  Purchase #4 $173.92   13.348%   $197.1348   $197.13   $197.15   $197.10  
  Purchase #5 $172.35   8.113%   $186.3328   $186.33   $186.35   $186.30  
  Purchase #6 $153.51   4.391%   $160.2506   $160.25   $160.25   $160.30  
  Purchase #7 $195.29   3.237%   $201.6115   $201.61   $201.60   $201.60  
  7 purchase totals = $1,214.11       $1,325.4137   $1,325.41   $1,325.45   $1,325.40