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 $29.26   11.310%   $32.5693   $32.57   $32.55   $32.60  
  Purchase #2 $62.91   12.527%   $70.7907   $70.79   $70.80   $70.80  
  Purchase #3 $102.66   3.586%   $106.3414   $106.34   $106.35   $106.30  
  Purchase #4 $209.27   8.702%   $227.4807   $227.48   $227.50   $227.50  
  Purchase #5 $11.95   13.429%   $13.5548   $13.55   $13.55   $13.60  
  Purchase #6 $213.90   5.146%   $224.9073   $224.91   $224.90   $224.90  
  Purchase #7 $52.64   7.118%   $56.3869   $56.39   $56.40   $56.40  
  7 purchase totals = $682.59       $732.0311   $732.03   $732.05   $732.10