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 $214.67   13.647%   $243.966   $243.97   $243.95   $244.00  
  Purchase #2 $33.59   5.607%   $35.4734   $35.47   $35.45   $35.50  
  Purchase #3 $200.95   7.820%   $216.6643   $216.66   $216.65   $216.70  
  Purchase #4 $169.34   3.516%   $175.294   $175.29   $175.30   $175.30  
  Purchase #5 $88.76   5.231%   $93.403   $93.40   $93.40   $93.40  
  Purchase #6 $75.54   4.180%   $78.6976   $78.70   $78.70   $78.70  
  Purchase #7 $51.73   3.315%   $53.4448   $53.44   $53.45   $53.40  
  7 purchase totals = $834.58       $896.9431   $896.93   $896.90   $897.00