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 $94.49   9.148%   $103.1339   $103.13   $103.15   $103.10  
  Purchase #2 $179.68   13.501%   $203.9386   $203.94   $203.95   $203.90  
  Purchase #3 $30.68   13.586%   $34.8482   $34.85   $34.85   $34.80  
  Purchase #4 $208.63   4.379%   $217.7659   $217.77   $217.75   $217.80  
  Purchase #5 $58.76   3.816%   $61.0023   $61.00   $61.00   $61.00  
  Purchase #6 $140.87   13.318%   $159.6311   $159.63   $159.65   $159.60  
  Purchase #7 $238.83   8.518%   $259.1735   $259.17   $259.15   $259.20  
  7 purchase totals = $951.94       $1,039.4935   $1,039.49   $1,039.50   $1,039.40