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 $208.55   8.775%   $226.8503   $226.85   $226.85   $226.90  
  Purchase #2 $116.89   13.516%   $132.6889   $132.69   $132.70   $132.70  
  Purchase #3 $91.54   5.663%   $96.7239   $96.72   $96.70   $96.70  
  Purchase #4 $116.26   11.418%   $129.5346   $129.53   $129.55   $129.50  
  Purchase #5 $195.97   9.692%   $214.9634   $214.96   $214.95   $215.00  
  Purchase #6 $174.83   11.528%   $194.9844   $194.98   $195.00   $195.00  
  Purchase #7 $23.40   3.717%   $24.2698   $24.27   $24.25   $24.30  
  7 purchase totals = $927.44       $1,020.0153   $1,020.00   $1,020.00   $1,020.10