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 $219.94   12.689%   $247.8482   $247.85   $247.85   $247.80  
  Purchase #2 $150.59   3.524%   $155.8968   $155.90   $155.90   $155.90  
  Purchase #3 $102.81   11.808%   $114.9498   $114.95   $114.95   $114.90  
  Purchase #4 $206.79   5.294%   $217.7375   $217.74   $217.75   $217.70  
  Purchase #5 $147.74   3.558%   $152.9966   $153.00   $153.00   $153.00  
  Purchase #6 $164.44   3.291%   $169.8517   $169.85   $169.85   $169.90  
  Purchase #7 $141.40   6.804%   $151.0209   $151.02   $151.00   $151.00  
  7 purchase totals = $1,133.71       $1,210.3015   $1,210.31   $1,210.30   $1,210.20