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 $65.80   10.601%   $72.7755   $72.78   $72.80   $72.80  
  Purchase #2 $227.42   10.614%   $251.5584   $251.56   $251.55   $251.60  
  Purchase #3 $146.90   5.343%   $154.7489   $154.75   $154.75   $154.70  
  Purchase #4 $31.91   4.823%   $33.449   $33.45   $33.45   $33.40  
  Purchase #5 $79.58   10.124%   $87.6367   $87.64   $87.65   $87.60  
  Purchase #6 $163.48   3.198%   $168.7081   $168.71   $168.70   $168.70  
  Purchase #7 $26.33   5.557%   $27.7932   $27.79   $27.80   $27.80  
  7 purchase totals = $741.42       $796.6698   $796.68   $796.70   $796.60