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 $88.53   10.745%   $98.0425   $98.04   $98.05   $98.00  
  Purchase #2 $54.77   13.662%   $62.2527   $62.25   $62.25   $62.30  
  Purchase #3 $47.58   4.464%   $49.704   $49.70   $49.70   $49.70  
  Purchase #4 $246.80   13.379%   $279.8194   $279.82   $279.80   $279.80  
  Purchase #5 $147.41   6.135%   $156.4536   $156.45   $156.45   $156.50  
  Purchase #6 $181.97   12.622%   $204.9383   $204.94   $204.95   $204.90  
  Purchase #7 $129.50   3.859%   $134.4974   $134.50   $134.50   $134.50  
  7 purchase totals = $896.56       $985.7079   $985.70   $985.70   $985.70