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 $32.74   9.393%   $35.8153   $35.82   $35.80   $35.80  
  Purchase #2 $232.68   4.207%   $242.4688   $242.47   $242.45   $242.50  
  Purchase #3 $211.63   7.557%   $227.6229   $227.62   $227.60   $227.60  
  Purchase #4 $239.72   12.456%   $269.5795   $269.58   $269.60   $269.60  
  Purchase #5 $97.63   8.665%   $106.0896   $106.09   $106.10   $106.10  
  Purchase #6 $69.35   11.337%   $77.2122   $77.21   $77.20   $77.20  
  Purchase #7 $53.59   13.140%   $60.6317   $60.63   $60.65   $60.60  
  7 purchase totals = $937.34       $1,019.4200   $1,019.42   $1,019.40   $1,019.40