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 $14.40   8.228%   $15.5848   $15.58   $15.60   $15.60  
  Purchase #2 $122.56   3.828%   $127.2516   $127.25   $127.25   $127.30  
  Purchase #3 $45.57   11.239%   $50.6916   $50.69   $50.70   $50.70  
  Purchase #4 $57.48   5.482%   $60.6311   $60.63   $60.65   $60.60  
  Purchase #5 $232.43   9.432%   $254.3528   $254.35   $254.35   $254.40  
  Purchase #6 $225.84   3.839%   $234.51   $234.51   $234.50   $234.50  
  Purchase #7 $211.67   6.106%   $224.5946   $224.59   $224.60   $224.60  
  7 purchase totals = $909.95       $967.6165   $967.60   $967.65   $967.70