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 $247.98   4.463%   $259.0473   $259.05   $259.05   $259.00  
  Purchase #2 $125.98   5.118%   $132.4277   $132.43   $132.45   $132.40  
  Purchase #3 $202.38   8.505%   $219.5924   $219.59   $219.60   $219.60  
  Purchase #4 $149.43   7.128%   $160.0814   $160.08   $160.10   $160.10  
  Purchase #5 $137.47   12.366%   $154.4695   $154.47   $154.45   $154.50  
  Purchase #6 $185.94   5.159%   $195.5326   $195.53   $195.55   $195.50  
  Purchase #7 $20.27   4.194%   $21.1201   $21.12   $21.10   $21.10  
  7 purchase totals = $1,069.45       $1,142.2710   $1,142.27   $1,142.30   $1,142.20