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 $86.38   13.595%   $98.1234   $98.12   $98.10   $98.10  
  Purchase #2 $130.37   9.504%   $142.7604   $142.76   $142.75   $142.80  
  Purchase #3 $230.63   8.171%   $249.4748   $249.47   $249.45   $249.50  
  Purchase #4 $207.60   9.588%   $227.5047   $227.50   $227.50   $227.50  
  Purchase #5 $68.93   11.445%   $76.819   $76.82   $76.80   $76.80  
  Purchase #6 $186.51   9.615%   $204.4429   $204.44   $204.45   $204.40  
  Purchase #7 $87.76   6.421%   $93.3951   $93.40   $93.40   $93.40  
  7 purchase totals = $998.18       $1,092.5203   $1,092.51   $1,092.45   $1,092.50