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 $61.49   3.563%   $63.6809   $63.68   $63.70   $63.70  
  Purchase #2 $217.52   4.869%   $228.111   $228.11   $228.10   $228.10  
  Purchase #3 $104.30   9.592%   $114.3045   $114.30   $114.30   $114.30  
  Purchase #4 $160.64   12.615%   $180.9047   $180.90   $180.90   $180.90  
  Purchase #5 $209.63   11.356%   $233.4356   $233.44   $233.45   $233.40  
  Purchase #6 $113.88   9.184%   $124.3387   $124.34   $124.35   $124.30  
  Purchase #7 $35.45   11.528%   $39.5367   $39.54   $39.55   $39.50  
  7 purchase totals = $902.91       $984.3121   $984.31   $984.35   $984.20