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 $136.61   13.622%   $155.219   $155.22   $155.20   $155.20  
  Purchase #2 $242.32   11.347%   $269.8161   $269.82   $269.80   $269.80  
  Purchase #3 $87.81   4.709%   $91.945   $91.95   $91.95   $91.90  
  Purchase #4 $125.88   9.130%   $137.3728   $137.37   $137.35   $137.40  
  Purchase #5 $140.78   10.383%   $155.3972   $155.40   $155.40   $155.40  
  Purchase #6 $240.45   4.491%   $251.2486   $251.25   $251.25   $251.20  
  Purchase #7 $20.72   11.634%   $23.1306   $23.13   $23.15   $23.10  
  7 purchase totals = $994.57       $1,084.1293   $1,084.14   $1,084.10   $1,084.00