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 $93.69   5.162%   $98.5263   $98.53   $98.55   $98.50  
  Purchase #2 $109.97   11.642%   $122.7727   $122.77   $122.75   $122.80  
  Purchase #3 $112.33   6.839%   $120.0122   $120.01   $120.00   $120.00  
  Purchase #4 $185.79   11.310%   $206.8028   $206.80   $206.80   $206.80  
  Purchase #5 $84.48   5.311%   $88.9667   $88.97   $88.95   $89.00  
  Purchase #6 $53.70   10.175%   $59.164   $59.16   $59.15   $59.20  
  Purchase #7 $237.81   7.673%   $256.0572   $256.06   $256.05   $256.10  
  7 purchase totals = $877.77       $952.3019   $952.30   $952.25   $952.40