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 $240.95   11.102%   $267.7003   $267.70   $267.70   $267.70  
  Purchase #2 $212.88   9.543%   $233.1951   $233.20   $233.20   $233.20  
  Purchase #3 $221.91   11.378%   $247.1589   $247.16   $247.15   $247.20  
  Purchase #4 $150.84   11.119%   $167.6119   $167.61   $167.60   $167.60  
  Purchase #5 $89.92   11.704%   $100.4442   $100.44   $100.45   $100.40  
  Purchase #6 $205.31   4.536%   $214.6229   $214.62   $214.60   $214.60  
  Purchase #7 $133.64   6.414%   $142.2117   $142.21   $142.20   $142.20  
  7 purchase totals = $1,255.45       $1,372.9450   $1,372.94   $1,372.90   $1,372.90