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 $163.27   3.757%   $169.4041   $169.40   $169.40   $169.40  
  Purchase #2 $147.71   3.378%   $152.6996   $152.70   $152.70   $152.70  
  Purchase #3 $55.97   3.153%   $57.7347   $57.73   $57.75   $57.70  
  Purchase #4 $82.89   3.659%   $85.9229   $85.92   $85.90   $85.90  
  Purchase #5 $101.73   7.559%   $109.4198   $109.42   $109.40   $109.40  
  Purchase #6 $92.95   10.251%   $102.4783   $102.48   $102.50   $102.50  
  Purchase #7 $17.80   3.586%   $18.4383   $18.44   $18.45   $18.40  
  7 purchase totals = $662.32       $696.0977   $696.09   $696.10   $696.00