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 $198.76   5.542%   $209.7753   $209.78   $209.80   $209.80  
  Purchase #2 $19.42   4.525%   $20.2988   $20.30   $20.30   $20.30  
  Purchase #3 $60.42   10.839%   $66.9689   $66.97   $66.95   $67.00  
  Purchase #4 $111.53   6.106%   $118.34   $118.34   $118.35   $118.30  
  Purchase #5 $86.68   7.644%   $93.3058   $93.31   $93.30   $93.30  
  Purchase #6 $214.81   7.485%   $230.8885   $230.89   $230.90   $230.90  
  Purchase #7 $20.76   6.126%   $22.0318   $22.03   $22.05   $22.00  
  7 purchase totals = $712.38       $761.6091   $761.62   $761.65   $761.60