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 $231.59   10.293%   $255.4276   $255.43   $255.45   $255.40  
  Purchase #2 $60.86   7.449%   $65.3935   $65.39   $65.40   $65.40  
  Purchase #3 $167.94   3.559%   $173.917   $173.92   $173.90   $173.90  
  Purchase #4 $145.98   5.829%   $154.4892   $154.49   $154.50   $154.50  
  Purchase #5 $233.55   4.659%   $244.4311   $244.43   $244.45   $244.40  
  Purchase #6 $21.75   3.174%   $22.4403   $22.44   $22.45   $22.40  
  Purchase #7 $98.90   11.466%   $110.2399   $110.24   $110.25   $110.20  
  7 purchase totals = $960.57       $1,026.3386   $1,026.34   $1,026.40   $1,026.20