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 $114.94   10.771%   $127.3202   $127.32   $127.30   $127.30  
  Purchase #2 $165.94   5.428%   $174.9472   $174.95   $174.95   $174.90  
  Purchase #3 $151.86   11.660%   $169.5669   $169.57   $169.55   $169.60  
  Purchase #4 $27.57   8.864%   $30.0138   $30.01   $30.00   $30.00  
  Purchase #5 $45.25   6.707%   $48.2849   $48.28   $48.30   $48.30  
  Purchase #6 $106.99   8.641%   $116.235   $116.24   $116.25   $116.20  
  Purchase #7 $228.52   7.256%   $245.1014   $245.10   $245.10   $245.10  
  7 purchase totals = $841.07       $911.4694   $911.47   $911.45   $911.40