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 $54.96   7.644%   $59.1611   $59.16   $59.15   $59.20  
  Purchase #2 $56.88   7.253%   $61.0055   $61.01   $61.00   $61.00  
  Purchase #3 $48.89   4.856%   $51.2641   $51.26   $51.25   $51.30  
  Purchase #4 $14.71   13.276%   $16.6629   $16.66   $16.65   $16.70  
  Purchase #5 $95.60   7.645%   $102.9086   $102.91   $102.90   $102.90  
  Purchase #6 $212.69   12.477%   $239.2273   $239.23   $239.25   $239.20  
  Purchase #7 $168.73   4.470%   $176.2722   $176.27   $176.25   $176.30  
  7 purchase totals = $652.46       $706.5017   $706.50   $706.45   $706.60