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 $211.99   6.663%   $226.1149   $226.11   $226.10   $226.10  
  Purchase #2 $78.25   5.765%   $82.7611   $82.76   $82.75   $82.80  
  Purchase #3 $73.86   7.298%   $79.2503   $79.25   $79.25   $79.30  
  Purchase #4 $48.31   9.363%   $52.8333   $52.83   $52.85   $52.80  
  Purchase #5 $66.43   8.222%   $71.8919   $71.89   $71.90   $71.90  
  Purchase #6 $20.94   11.678%   $23.3854   $23.39   $23.40   $23.40  
  Purchase #7 $60.47   9.332%   $66.1131   $66.11   $66.10   $66.10  
  7 purchase totals = $560.25       $602.3500   $602.34   $602.35   $602.40