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 $206.57   8.706%   $224.554   $224.55   $224.55   $224.60  
  Purchase #2 $13.97   4.681%   $14.6239   $14.62   $14.60   $14.60  
  Purchase #3 $157.45   9.506%   $172.4172   $172.42   $172.40   $172.40  
  Purchase #4 $191.34   13.346%   $216.8762   $216.88   $216.90   $216.90  
  Purchase #5 $7.76   7.477%   $8.3402   $8.34   $8.35   $8.30  
  Purchase #6 $72.48   9.313%   $79.2301   $79.23   $79.25   $79.20  
  Purchase #7 $247.31   8.786%   $269.0387   $269.04   $269.05   $269.00  
  7 purchase totals = $896.88       $985.0803   $985.08   $985.10   $985.00