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 $55.60   11.543%   $62.0179   $62.02   $62.00   $62.00  
  Purchase #2 $148.97   9.413%   $162.9925   $162.99   $163.00   $163.00  
  Purchase #3 $232.32   8.197%   $251.3633   $251.36   $251.35   $251.40  
  Purchase #4 $116.29   9.117%   $126.8922   $126.89   $126.90   $126.90  
  Purchase #5 $104.25   3.416%   $107.8112   $107.81   $107.80   $107.80  
  Purchase #6 $124.97   3.552%   $129.4089   $129.41   $129.40   $129.40  
  Purchase #7 $76.87   12.749%   $86.6702   $86.67   $86.65   $86.70  
  7 purchase totals = $859.27       $927.1562   $927.15   $927.10   $927.20