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 $206.43   3.820%   $214.3156   $214.32   $214.30   $214.30  
  Purchase #2 $224.96   9.804%   $247.0151   $247.02   $247.00   $247.00  
  Purchase #3 $167.82   9.770%   $184.216   $184.22   $184.20   $184.20  
  Purchase #4 $45.82   8.256%   $49.6029   $49.60   $49.60   $49.60  
  Purchase #5 $179.98   8.604%   $195.4655   $195.47   $195.45   $195.50  
  Purchase #6 $60.31   7.206%   $64.6559   $64.66   $64.65   $64.70  
  Purchase #7 $37.61   13.616%   $42.731   $42.73   $42.75   $42.70  
  7 purchase totals = $922.93       $998.0020   $998.02   $997.95   $998.00