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 $60.93   4.652%   $63.7645   $63.76   $63.75   $63.80  
  Purchase #2 $63.74   8.161%   $68.9418   $68.94   $68.95   $68.90  
  Purchase #3 $71.99   3.482%   $74.4967   $74.50   $74.50   $74.50  
  Purchase #4 $145.97   8.648%   $158.5935   $158.59   $158.60   $158.60  
  Purchase #5 $211.40   9.831%   $232.1827   $232.18   $232.20   $232.20  
  Purchase #6 $9.74   6.560%   $10.3789   $10.38   $10.40   $10.40  
  Purchase #7 $181.31   8.582%   $196.87   $196.87   $196.85   $196.90  
  7 purchase totals = $745.08       $805.2281   $805.22   $805.25   $805.30