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 $167.91   8.361%   $181.949   $181.95   $181.95   $181.90  
  Purchase #2 $19.48   13.196%   $22.0506   $22.05   $22.05   $22.10  
  Purchase #3 $72.91   4.655%   $76.304   $76.30   $76.30   $76.30  
  Purchase #4 $117.32   8.761%   $127.5984   $127.60   $127.60   $127.60  
  Purchase #5 $74.28   13.340%   $84.189   $84.19   $84.20   $84.20  
  Purchase #6 $59.93   11.686%   $66.9334   $66.93   $66.95   $66.90  
  Purchase #7 $194.64   6.214%   $206.7349   $206.73   $206.75   $206.70  
  7 purchase totals = $706.47       $765.7593   $765.75   $765.80   $765.70