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 $223.83   9.826%   $245.8235   $245.82   $245.80   $245.80  
  Purchase #2 $119.26   4.544%   $124.6792   $124.68   $124.70   $124.70  
  Purchase #3 $158.29   9.177%   $172.8163   $172.82   $172.80   $172.80  
  Purchase #4 $192.52   11.673%   $214.9929   $214.99   $215.00   $215.00  
  Purchase #5 $106.92   7.761%   $115.2181   $115.22   $115.20   $115.20  
  Purchase #6 $162.93   9.178%   $177.8837   $177.88   $177.90   $177.90  
  Purchase #7 $22.67   8.575%   $24.614   $24.61   $24.60   $24.60  
  7 purchase totals = $986.42       $1,076.0277   $1,076.02   $1,076.00   $1,076.00