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 $47.94   4.309%   $50.0057   $50.01   $50.00   $50.00  
  Purchase #2 $224.82   7.779%   $242.3087   $242.31   $242.30   $242.30  
  Purchase #3 $169.40   11.381%   $188.6794   $188.68   $188.70   $188.70  
  Purchase #4 $107.88   7.720%   $116.2083   $116.21   $116.20   $116.20  
  Purchase #5 $196.62   3.697%   $203.889   $203.89   $203.90   $203.90  
  Purchase #6 $111.32   3.470%   $115.1828   $115.18   $115.20   $115.20  
  Purchase #7 $32.71   3.137%   $33.7361   $33.74   $33.75   $33.70  
  7 purchase totals = $890.69       $950.0100   $950.02   $950.05   $950.00