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 $231.92   6.351%   $246.6492   $246.65   $246.65   $246.60  
  Purchase #2 $24.63   5.505%   $25.9859   $25.99   $26.00   $26.00  
  Purchase #3 $79.41   5.382%   $83.6838   $83.68   $83.70   $83.70  
  Purchase #4 $151.32   10.679%   $167.4795   $167.48   $167.50   $167.50  
  Purchase #5 $203.38   9.429%   $222.5567   $222.56   $222.55   $222.60  
  Purchase #6 $236.64   13.755%   $269.1898   $269.19   $269.20   $269.20  
  Purchase #7 $40.66   9.607%   $44.5662   $44.57   $44.55   $44.60  
  7 purchase totals = $967.96       $1,060.1111   $1,060.12   $1,060.15   $1,060.20