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 $82.87   6.487%   $88.2458   $88.25   $88.25   $88.20  
  Purchase #2 $148.28   9.796%   $162.8055   $162.81   $162.80   $162.80  
  Purchase #3 $171.80   3.232%   $177.3526   $177.35   $177.35   $177.40  
  Purchase #4 $228.44   6.326%   $242.8911   $242.89   $242.90   $242.90  
  Purchase #5 $163.86   4.297%   $170.9011   $170.90   $170.90   $170.90  
  Purchase #6 $151.98   9.317%   $166.14   $166.14   $166.15   $166.10  
  Purchase #7 $30.73   6.104%   $32.6058   $32.61   $32.60   $32.60  
  7 purchase totals = $977.96       $1,040.9419   $1,040.95   $1,040.95   $1,040.90