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 $248.66   11.363%   $276.9152   $276.92   $276.90   $276.90  
  Purchase #2 $195.72   10.649%   $216.5622   $216.56   $216.55   $216.60  
  Purchase #3 $62.38   12.111%   $69.9348   $69.93   $69.95   $69.90  
  Purchase #4 $231.78   4.593%   $242.4257   $242.43   $242.45   $242.40  
  Purchase #5 $162.26   8.368%   $175.8379   $175.84   $175.85   $175.80  
  Purchase #6 $128.51   7.607%   $138.2858   $138.29   $138.30   $138.30  
  Purchase #7 $71.72   4.230%   $74.7538   $74.75   $74.75   $74.80  
  7 purchase totals = $1,101.03       $1,194.7154   $1,194.72   $1,194.75   $1,194.70