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 $185.91   12.156%   $208.5092   $208.51   $208.50   $208.50  
  Purchase #2 $161.97   6.401%   $172.3377   $172.34   $172.35   $172.30  
  Purchase #3 $154.77   11.818%   $173.0607   $173.06   $173.05   $173.10  
  Purchase #4 $58.44   7.175%   $62.6331   $62.63   $62.65   $62.60  
  Purchase #5 $225.73   8.703%   $245.3753   $245.38   $245.40   $245.40  
  Purchase #6 $21.84   12.142%   $24.4918   $24.49   $24.50   $24.50  
  Purchase #7 $195.82   10.575%   $216.528   $216.53   $216.55   $216.50  
  7 purchase totals = $1,004.48       $1,102.9358   $1,102.94   $1,103.00   $1,102.90