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 $227.37   10.411%   $251.0415   $251.04   $251.05   $251.00  
  Purchase #2 $166.82   11.314%   $185.694   $185.69   $185.70   $185.70  
  Purchase #3 $155.69   4.533%   $162.7474   $162.75   $162.75   $162.70  
  Purchase #4 $101.33   4.284%   $105.671   $105.67   $105.65   $105.70  
  Purchase #5 $235.32   4.551%   $246.0294   $246.03   $246.05   $246.00  
  Purchase #6 $18.55   3.400%   $19.1807   $19.18   $19.20   $19.20  
  Purchase #7 $102.91   4.350%   $107.3866   $107.39   $107.40   $107.40  
  7 purchase totals = $1,007.99       $1,077.7506   $1,077.75   $1,077.80   $1,077.70