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 $46.88   13.167%   $53.0527   $53.05   $53.05   $53.10  
  Purchase #2 $66.43   4.275%   $69.2699   $69.27   $69.25   $69.30  
  Purchase #3 $167.36   10.760%   $185.3679   $185.37   $185.35   $185.40  
  Purchase #4 $228.91   3.172%   $236.171   $236.17   $236.15   $236.20  
  Purchase #5 $233.73   5.622%   $246.8703   $246.87   $246.85   $246.90  
  Purchase #6 $202.50   9.489%   $221.7152   $221.72   $221.70   $221.70  
  Purchase #7 $14.68   12.737%   $16.5498   $16.55   $16.55   $16.50  
  7 purchase totals = $960.49       $1,028.9968   $1,029.00   $1,028.90   $1,029.10