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 $216.75   10.600%   $239.7255   $239.73   $239.75   $239.70  
  Purchase #2 $167.49   9.553%   $183.4903   $183.49   $183.50   $183.50  
  Purchase #3 $117.94   4.793%   $123.5929   $123.59   $123.60   $123.60  
  Purchase #4 $44.80   13.558%   $50.874   $50.87   $50.85   $50.90  
  Purchase #5 $13.85   7.140%   $14.8389   $14.84   $14.85   $14.80  
  Purchase #6 $150.35   6.547%   $160.1934   $160.19   $160.20   $160.20  
  Purchase #7 $47.73   6.351%   $50.7613   $50.76   $50.75   $50.80  
  7 purchase totals = $758.91       $823.4763   $823.47   $823.50   $823.50