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 $249.97   6.575%   $266.4055   $266.41   $266.40   $266.40  
  Purchase #2 $58.91   7.209%   $63.1568   $63.16   $63.15   $63.20  
  Purchase #3 $186.93   13.539%   $212.2385   $212.24   $212.25   $212.20  
  Purchase #4 $149.57   4.494%   $156.2917   $156.29   $156.30   $156.30  
  Purchase #5 $84.38   6.191%   $89.604   $89.60   $89.60   $89.60  
  Purchase #6 $37.33   4.835%   $39.1349   $39.13   $39.15   $39.10  
  Purchase #7 $186.29   11.602%   $207.9034   $207.90   $207.90   $207.90  
  7 purchase totals = $953.38       $1,034.7348   $1,034.73   $1,034.75   $1,034.70