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 $56.46   5.120%   $59.3508   $59.35   $59.35   $59.40  
  Purchase #2 $226.45   11.311%   $252.0638   $252.06   $252.05   $252.10  
  Purchase #3 $58.40   7.139%   $62.5692   $62.57   $62.55   $62.60  
  Purchase #4 $106.42   10.333%   $117.4164   $117.42   $117.40   $117.40  
  Purchase #5 $130.55   7.477%   $140.3112   $140.31   $140.30   $140.30  
  Purchase #6 $230.37   3.240%   $237.834   $237.83   $237.85   $237.80  
  Purchase #7 $78.77   11.632%   $87.9325   $87.93   $87.95   $87.90  
  7 purchase totals = $887.42       $957.4779   $957.47   $957.45   $957.50