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 $148.87   12.426%   $167.3686   $167.37   $167.35   $167.40  
  Purchase #2 $237.98   10.384%   $262.6918   $262.69   $262.70   $262.70  
  Purchase #3 $197.51   5.216%   $207.8121   $207.81   $207.80   $207.80  
  Purchase #4 $240.66   4.234%   $250.8495   $250.85   $250.85   $250.80  
  Purchase #5 $71.80   13.167%   $81.2539   $81.25   $81.25   $81.30  
  Purchase #6 $51.50   7.323%   $55.2713   $55.27   $55.25   $55.30  
  Purchase #7 $112.43   4.156%   $117.1026   $117.10   $117.10   $117.10  
  7 purchase totals = $1,060.75       $1,142.3498   $1,142.34   $1,142.30   $1,142.40