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 $86.57   13.231%   $98.0241   $98.02   $98.00   $98.00  
  Purchase #2 $238.67   7.443%   $256.4342   $256.43   $256.45   $256.40  
  Purchase #3 $65.42   12.157%   $73.3731   $73.37   $73.35   $73.40  
  Purchase #4 $93.70   8.408%   $101.5783   $101.58   $101.60   $101.60  
  Purchase #5 $60.74   7.845%   $65.5051   $65.51   $65.50   $65.50  
  Purchase #6 $220.50   3.590%   $228.416   $228.42   $228.40   $228.40  
  Purchase #7 $16.55   7.296%   $17.7575   $17.76   $17.75   $17.80  
  7 purchase totals = $782.15       $841.0883   $841.09   $841.05   $841.10