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 $233.63   8.282%   $252.9792   $252.98   $253.00   $253.00  
  Purchase #2 $175.70   5.861%   $185.9978   $186.00   $186.00   $186.00  
  Purchase #3 $177.76   10.241%   $195.9644   $195.96   $195.95   $196.00  
  Purchase #4 $32.87   9.193%   $35.8917   $35.89   $35.90   $35.90  
  Purchase #5 $75.65   9.225%   $82.6287   $82.63   $82.65   $82.60  
  Purchase #6 $184.60   4.317%   $192.5692   $192.57   $192.55   $192.60  
  Purchase #7 $47.82   5.541%   $50.4697   $50.47   $50.45   $50.50  
  7 purchase totals = $928.03       $996.5007   $996.50   $996.50   $996.60