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 $9.37   5.318%   $9.8683   $9.87   $9.85   $9.90  
  Purchase #2 $7.36   10.612%   $8.141   $8.14   $8.15   $8.10  
  Purchase #3 $71.94   7.720%   $77.4938   $77.49   $77.50   $77.50  
  Purchase #4 $223.72   4.709%   $234.255   $234.26   $234.25   $234.30  
  Purchase #5 $154.50   6.467%   $164.4915   $164.49   $164.50   $164.50  
  Purchase #6 $63.52   3.811%   $65.9407   $65.94   $65.95   $65.90  
  Purchase #7 $239.33   10.522%   $264.5123   $264.51   $264.50   $264.50  
  7 purchase totals = $769.74       $824.7026   $824.70   $824.70   $824.70