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 $8.78   4.322%   $9.1595   $9.16   $9.15   $9.20  
  Purchase #2 $34.71   9.570%   $38.0317   $38.03   $38.05   $38.00  
  Purchase #3 $101.43   9.799%   $111.3691   $111.37   $111.35   $111.40  
  Purchase #4 $32.30   3.179%   $33.3268   $33.33   $33.35   $33.30  
  Purchase #5 $129.27   9.438%   $141.4705   $141.47   $141.45   $141.50  
  Purchase #6 $74.76   3.626%   $77.4708   $77.47   $77.45   $77.50  
  Purchase #7 $95.63   11.599%   $106.7221   $106.72   $106.70   $106.70  
  7 purchase totals = $476.88       $517.5505   $517.55   $517.50   $517.60