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 $214.51   10.613%   $237.2759   $237.28   $237.30   $237.30  
  Purchase #2 $250.45   11.426%   $279.0664   $279.07   $279.05   $279.10  
  Purchase #3 $183.66   5.567%   $193.8844   $193.88   $193.90   $193.90  
  Purchase #4 $59.78   13.183%   $67.6608   $67.66   $67.65   $67.70  
  Purchase #5 $131.97   11.759%   $147.4884   $147.49   $147.50   $147.50  
  Purchase #6 $109.62   8.256%   $118.6702   $118.67   $118.65   $118.70  
  Purchase #7 $13.89   8.781%   $15.1097   $15.11   $15.10   $15.10  
  7 purchase totals = $963.88       $1,059.1558   $1,059.16   $1,059.15   $1,059.30