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 $219.36   10.149%   $241.6228   $241.62   $241.60   $241.60  
  Purchase #2 $203.41   9.537%   $222.8092   $222.81   $222.80   $222.80  
  Purchase #3 $238.70   11.105%   $265.2076   $265.21   $265.20   $265.20  
  Purchase #4 $123.31   5.728%   $130.3732   $130.37   $130.35   $130.40  
  Purchase #5 $18.55   6.615%   $19.7771   $19.78   $19.80   $19.80  
  Purchase #6 $84.94   7.727%   $91.5033   $91.50   $91.50   $91.50  
  Purchase #7 $62.28   3.396%   $64.395   $64.40   $64.40   $64.40  
  7 purchase totals = $950.55       $1,035.6882   $1,035.69   $1,035.65   $1,035.70