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 $58.87   8.852%   $64.0812   $64.08   $64.10   $64.10  
  Purchase #2 $190.80   4.744%   $199.8516   $199.85   $199.85   $199.90  
  Purchase #3 $186.60   11.511%   $208.0795   $208.08   $208.10   $208.10  
  Purchase #4 $158.71   10.166%   $174.8445   $174.84   $174.85   $174.80  
  Purchase #5 $76.72   9.223%   $83.7959   $83.80   $83.80   $83.80  
  Purchase #6 $239.37   13.273%   $271.1416   $271.14   $271.15   $271.10  
  Purchase #7 $46.60   7.720%   $50.1975   $50.20   $50.20   $50.20  
  7 purchase totals = $957.67       $1,051.9918   $1,051.99   $1,052.05   $1,052.00