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 $237.47   13.153%   $268.7044   $268.70   $268.70   $268.70  
  Purchase #2 $136.97   6.505%   $145.8799   $145.88   $145.90   $145.90  
  Purchase #3 $50.83   7.672%   $54.7297   $54.73   $54.75   $54.70  
  Purchase #4 $212.26   9.233%   $231.858   $231.86   $231.85   $231.90  
  Purchase #5 $115.53   6.434%   $122.9632   $122.96   $122.95   $123.00  
  Purchase #6 $226.73   5.410%   $238.9961   $239.00   $239.00   $239.00  
  Purchase #7 $6.27   5.299%   $6.6022   $6.60   $6.60   $6.60  
  7 purchase totals = $986.06       $1,069.7335   $1,069.73   $1,069.75   $1,069.80