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 $249.34   7.196%   $267.2825   $267.28   $267.30   $267.30  
  Purchase #2 $152.97   9.770%   $167.9152   $167.92   $167.90   $167.90  
  Purchase #3 $119.99   11.491%   $133.7781   $133.78   $133.80   $133.80  
  Purchase #4 $82.29   3.683%   $85.3207   $85.32   $85.30   $85.30  
  Purchase #5 $206.62   6.867%   $220.8086   $220.81   $220.80   $220.80  
  Purchase #6 $222.61   4.118%   $231.7771   $231.78   $231.80   $231.80  
  Purchase #7 $45.48   9.602%   $49.847   $49.85   $49.85   $49.80  
  7 purchase totals = $1,079.30       $1,156.7292   $1,156.74   $1,156.75   $1,156.70