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 $89.76   9.234%   $98.0484   $98.05   $98.05   $98.00  
  Purchase #2 $158.74   3.213%   $163.8403   $163.84   $163.85   $163.80  
  Purchase #3 $72.50   3.479%   $75.0223   $75.02   $75.00   $75.00  
  Purchase #4 $224.92   4.181%   $234.3239   $234.32   $234.30   $234.30  
  Purchase #5 $250.97   12.857%   $283.2372   $283.24   $283.25   $283.20  
  Purchase #6 $240.36   4.849%   $252.0151   $252.02   $252.00   $252.00  
  Purchase #7 $180.45   3.742%   $187.2024   $187.20   $187.20   $187.20  
  7 purchase totals = $1,217.70       $1,293.6896   $1,293.69   $1,293.65   $1,293.50