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 $240.33   3.724%   $249.2799   $249.28   $249.30   $249.30  
  Purchase #2 $165.49   9.446%   $181.1222   $181.12   $181.10   $181.10  
  Purchase #3 $22.78   7.861%   $24.5707   $24.57   $24.55   $24.60  
  Purchase #4 $95.42   4.524%   $99.7368   $99.74   $99.75   $99.70  
  Purchase #5 $206.25   3.378%   $213.2171   $213.22   $213.20   $213.20  
  Purchase #6 $206.28   10.615%   $228.1766   $228.18   $228.20   $228.20  
  Purchase #7 $24.65   8.376%   $26.7147   $26.71   $26.70   $26.70  
  7 purchase totals = $961.20       $1,022.8180   $1,022.82   $1,022.80   $1,022.80