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 $168.44   7.617%   $181.2701   $181.27   $181.25   $181.30  
  Purchase #2 $204.94   3.790%   $212.7072   $212.71   $212.70   $212.70  
  Purchase #3 $172.95   3.638%   $179.2419   $179.24   $179.25   $179.20  
  Purchase #4 $32.61   5.643%   $34.4502   $34.45   $34.45   $34.50  
  Purchase #5 $239.69   5.528%   $252.9401   $252.94   $252.95   $252.90  
  Purchase #6 $151.60   7.432%   $162.8669   $162.87   $162.85   $162.90  
  Purchase #7 $10.44   3.135%   $10.7673   $10.77   $10.75   $10.80  
  7 purchase totals = $980.67       $1,034.2437   $1,034.25   $1,034.20   $1,034.30