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 $186.48   11.722%   $208.3392   $208.34   $208.35   $208.30  
  Purchase #2 $203.37   7.635%   $218.8973   $218.90   $218.90   $218.90  
  Purchase #3 $66.85   13.493%   $75.8701   $75.87   $75.85   $75.90  
  Purchase #4 $198.84   7.681%   $214.1129   $214.11   $214.10   $214.10  
  Purchase #5 $60.83   3.444%   $62.925   $62.93   $62.95   $62.90  
  Purchase #6 $64.98   13.116%   $73.5028   $73.50   $73.50   $73.50  
  Purchase #7 $209.61   6.618%   $223.482   $223.48   $223.50   $223.50  
  7 purchase totals = $990.96       $1,077.1293   $1,077.13   $1,077.15   $1,077.10