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 $216.96   11.504%   $241.9191   $241.92   $241.90   $241.90  
  Purchase #2 $71.69   11.829%   $80.1702   $80.17   $80.15   $80.20  
  Purchase #3 $136.64   4.486%   $142.7697   $142.77   $142.75   $142.80  
  Purchase #4 $166.33   11.740%   $185.8571   $185.86   $185.85   $185.90  
  Purchase #5 $123.73   9.509%   $135.4955   $135.50   $135.50   $135.50  
  Purchase #6 $21.28   6.820%   $22.7313   $22.73   $22.75   $22.70  
  Purchase #7 $120.68   13.530%   $137.008   $137.01   $137.00   $137.00  
  7 purchase totals = $857.31       $945.9509   $945.96   $945.90   $946.00