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 $102.38   11.396%   $114.0472   $114.05   $114.05   $114.00  
  Purchase #2 $242.66   13.339%   $275.0284   $275.03   $275.05   $275.00  
  Purchase #3 $59.81   9.263%   $65.3502   $65.35   $65.35   $65.40  
  Purchase #4 $34.39   7.557%   $36.9889   $36.99   $37.00   $37.00  
  Purchase #5 $111.53   4.829%   $116.9158   $116.92   $116.90   $116.90  
  Purchase #6 $189.71   8.206%   $205.2776   $205.28   $205.30   $205.30  
  Purchase #7 $234.44   11.150%   $260.5801   $260.58   $260.60   $260.60  
  7 purchase totals = $974.92       $1,074.1882   $1,074.20   $1,074.25   $1,074.20