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 $58.89   11.493%   $65.6582   $65.66   $65.65   $65.70  
  Purchase #2 $50.31   6.266%   $53.4624   $53.46   $53.45   $53.50  
  Purchase #3 $233.68   8.708%   $254.0289   $254.03   $254.05   $254.00  
  Purchase #4 $236.90   13.669%   $269.2819   $269.28   $269.30   $269.30  
  Purchase #5 $192.25   11.309%   $213.9916   $213.99   $214.00   $214.00  
  Purchase #6 $16.91   9.817%   $18.5701   $18.57   $18.55   $18.60  
  Purchase #7 $124.55   7.374%   $133.7343   $133.73   $133.75   $133.70  
  7 purchase totals = $913.49       $1,008.7274   $1,008.72   $1,008.75   $1,008.80