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 $198.60   13.465%   $225.3415   $225.34   $225.35   $225.30  
  Purchase #2 $182.75   4.496%   $190.9664   $190.97   $190.95   $191.00  
  Purchase #3 $6.31   3.440%   $6.5271   $6.53   $6.55   $6.50  
  Purchase #4 $91.64   11.626%   $102.2941   $102.29   $102.30   $102.30  
  Purchase #5 $192.87   8.685%   $209.6208   $209.62   $209.60   $209.60  
  Purchase #6 $169.63   13.777%   $192.9999   $193.00   $193.00   $193.00  
  Purchase #7 $89.38   5.449%   $94.2503   $94.25   $94.25   $94.30  
  7 purchase totals = $931.18       $1,022.0001   $1,022.00   $1,022.00   $1,022.00