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 $82.31   12.866%   $92.9   $92.90   $92.90   $92.90  
  Purchase #2 $226.55   11.198%   $251.9191   $251.92   $251.90   $251.90  
  Purchase #3 $54.78   5.524%   $57.806   $57.81   $57.80   $57.80  
  Purchase #4 $234.89   10.775%   $260.1994   $260.20   $260.20   $260.20  
  Purchase #5 $126.46   11.109%   $140.5084   $140.51   $140.50   $140.50  
  Purchase #6 $39.67   4.477%   $41.446   $41.45   $41.45   $41.40  
  Purchase #7 $241.54   9.856%   $265.3462   $265.35   $265.35   $265.30  
  7 purchase totals = $1,006.20       $1,110.1251   $1,110.14   $1,110.10   $1,110.00