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 $51.41   12.686%   $57.9319   $57.93   $57.95   $57.90  
  Purchase #2 $207.82   7.214%   $222.8121   $222.81   $222.80   $222.80  
  Purchase #3 $101.68   7.485%   $109.2907   $109.29   $109.30   $109.30  
  Purchase #4 $16.74   11.440%   $18.6551   $18.66   $18.65   $18.70  
  Purchase #5 $163.69   3.817%   $169.938   $169.94   $169.95   $169.90  
  Purchase #6 $233.67   13.748%   $265.795   $265.80   $265.80   $265.80  
  Purchase #7 $142.60   12.450%   $160.3537   $160.35   $160.35   $160.40  
  7 purchase totals = $917.61       $1,004.7765   $1,004.78   $1,004.80   $1,004.80