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 $91.45   5.123%   $96.135   $96.14   $96.15   $96.10  
  Purchase #2 $232.47   11.432%   $259.046   $259.05   $259.05   $259.00  
  Purchase #3 $26.29   4.640%   $27.5099   $27.51   $27.50   $27.50  
  Purchase #4 $169.93   11.172%   $188.9146   $188.91   $188.90   $188.90  
  Purchase #5 $72.84   3.805%   $75.6116   $75.61   $75.60   $75.60  
  Purchase #6 $8.49   9.490%   $9.2957   $9.30   $9.30   $9.30  
  Purchase #7 $71.64   11.306%   $79.7396   $79.74   $79.75   $79.70  
  7 purchase totals = $673.11       $736.2524   $736.26   $736.25   $736.10