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 $197.91   6.242%   $210.2635   $210.26   $210.25   $210.30  
  Purchase #2 $218.32   3.216%   $225.3412   $225.34   $225.35   $225.30  
  Purchase #3 $54.59   9.172%   $59.597   $59.60   $59.60   $59.60  
  Purchase #4 $78.90   9.843%   $86.6661   $86.67   $86.65   $86.70  
  Purchase #5 $151.91   4.577%   $158.8629   $158.86   $158.85   $158.90  
  Purchase #6 $200.97   11.507%   $224.0956   $224.10   $224.10   $224.10  
  Purchase #7 $81.76   7.346%   $87.7661   $87.77   $87.75   $87.80  
  7 purchase totals = $984.36       $1,052.5924   $1,052.60   $1,052.55   $1,052.70