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 $245.88   7.274%   $263.7653   $263.77   $263.75   $263.80  
  Purchase #2 $168.44   11.139%   $187.2025   $187.20   $187.20   $187.20  
  Purchase #3 $234.82   9.125%   $256.2473   $256.25   $256.25   $256.20  
  Purchase #4 $85.44   12.652%   $96.2499   $96.25   $96.25   $96.20  
  Purchase #5 $18.93   3.812%   $19.6516   $19.65   $19.65   $19.70  
  Purchase #6 $56.86   8.526%   $61.7079   $61.71   $61.70   $61.70  
  Purchase #7 $161.78   3.319%   $167.1495   $167.15   $167.15   $167.10  
  7 purchase totals = $972.15       $1,051.9740   $1,051.98   $1,051.95   $1,051.90