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 $217.93   13.203%   $246.7033   $246.70   $246.70   $246.70  
  Purchase #2 $130.56   7.190%   $139.9473   $139.95   $139.95   $139.90  
  Purchase #3 $183.62   8.249%   $198.7668   $198.77   $198.75   $198.80  
  Purchase #4 $77.59   3.632%   $80.4081   $80.41   $80.40   $80.40  
  Purchase #5 $38.58   5.206%   $40.5885   $40.59   $40.60   $40.60  
  Purchase #6 $101.57   10.677%   $112.4146   $112.41   $112.40   $112.40  
  Purchase #7 $219.65   11.469%   $244.8417   $244.84   $244.85   $244.80  
  7 purchase totals = $969.50       $1,063.6703   $1,063.67   $1,063.65   $1,063.60