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 $45.84   6.238%   $48.6995   $48.70   $48.70   $48.70  
  Purchase #2 $240.31   8.218%   $260.0587   $260.06   $260.05   $260.10  
  Purchase #3 $95.72   3.622%   $99.187   $99.19   $99.20   $99.20  
  Purchase #4 $214.88   4.367%   $224.2638   $224.26   $224.25   $224.30  
  Purchase #5 $164.65   11.621%   $183.784   $183.78   $183.80   $183.80  
  Purchase #6 $175.30   6.557%   $186.7944   $186.79   $186.80   $186.80  
  Purchase #7 $48.39   10.734%   $53.5842   $53.58   $53.60   $53.60  
  7 purchase totals = $985.09       $1,056.3716   $1,056.36   $1,056.40   $1,056.50