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 $233.62   8.842%   $254.2767   $254.28   $254.30   $254.30  
  Purchase #2 $208.29   6.406%   $221.6331   $221.63   $221.65   $221.60  
  Purchase #3 $162.86   5.191%   $171.3141   $171.31   $171.30   $171.30  
  Purchase #4 $128.80   13.614%   $146.3348   $146.33   $146.35   $146.30  
  Purchase #5 $234.42   3.189%   $241.8957   $241.90   $241.90   $241.90  
  Purchase #6 $218.81   7.765%   $235.8006   $235.80   $235.80   $235.80  
  Purchase #7 $117.38   6.201%   $124.6587   $124.66   $124.65   $124.70  
  7 purchase totals = $1,304.18       $1,395.9137   $1,395.91   $1,395.95   $1,395.90