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 $94.87   3.770%   $98.4466   $98.45   $98.45   $98.40  
  Purchase #2 $239.93   8.311%   $259.8706   $259.87   $259.85   $259.90  
  Purchase #3 $169.30   10.423%   $186.9461   $186.95   $186.95   $186.90  
  Purchase #4 $88.39   3.296%   $91.3033   $91.30   $91.30   $91.30  
  Purchase #5 $206.66   8.316%   $223.8458   $223.85   $223.85   $223.80  
  Purchase #6 $223.27   5.446%   $235.4293   $235.43   $235.45   $235.40  
  Purchase #7 $12.50   4.812%   $13.1015   $13.10   $13.10   $13.10  
  7 purchase totals = $1,034.92       $1,108.9432   $1,108.95   $1,108.95   $1,108.80