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 $154.83   4.613%   $161.9723   $161.97   $161.95   $162.00  
  Purchase #2 $204.96   5.713%   $216.6694   $216.67   $216.65   $216.70  
  Purchase #3 $50.67   7.185%   $54.3106   $54.31   $54.30   $54.30  
  Purchase #4 $176.81   5.322%   $186.2198   $186.22   $186.20   $186.20  
  Purchase #5 $69.63   4.371%   $72.6735   $72.67   $72.65   $72.70  
  Purchase #6 $61.59   12.791%   $69.468   $69.47   $69.45   $69.50  
  Purchase #7 $192.70   9.465%   $210.9391   $210.94   $210.95   $210.90  
  7 purchase totals = $911.19       $972.2527   $972.25   $972.15   $972.30