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 $231.28   6.736%   $246.859   $246.86   $246.85   $246.90  
  Purchase #2 $64.79   6.764%   $69.1724   $69.17   $69.15   $69.20  
  Purchase #3 $63.93   11.109%   $71.032   $71.03   $71.05   $71.00  
  Purchase #4 $212.70   6.250%   $225.9938   $225.99   $226.00   $226.00  
  Purchase #5 $112.42   13.177%   $127.2336   $127.23   $127.25   $127.20  
  Purchase #6 $187.78   11.269%   $208.9409   $208.94   $208.95   $208.90  
  Purchase #7 $69.81   11.124%   $77.5757   $77.58   $77.60   $77.60  
  7 purchase totals = $942.71       $1,026.8074   $1,026.80   $1,026.85   $1,026.80