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 $89.74   6.572%   $95.6377   $95.64   $95.65   $95.60  
  Purchase #2 $160.94   8.146%   $174.0502   $174.05   $174.05   $174.10  
  Purchase #3 $214.38   7.503%   $230.4649   $230.46   $230.45   $230.50  
  Purchase #4 $116.45   10.120%   $128.2347   $128.23   $128.25   $128.20  
  Purchase #5 $231.97   3.580%   $240.2745   $240.27   $240.25   $240.30  
  Purchase #6 $250.30   6.345%   $266.1815   $266.18   $266.20   $266.20  
  Purchase #7 $159.35   7.247%   $170.8981   $170.90   $170.90   $170.90  
  7 purchase totals = $1,223.13       $1,305.7416   $1,305.73   $1,305.75   $1,305.80