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 $222.88   10.391%   $246.0395   $246.04   $246.05   $246.00  
  Purchase #2 $207.97   9.393%   $227.5046   $227.50   $227.50   $227.50  
  Purchase #3 $165.74   10.806%   $183.6499   $183.65   $183.65   $183.60  
  Purchase #4 $228.37   11.375%   $254.3471   $254.35   $254.35   $254.30  
  Purchase #5 $186.48   6.471%   $198.5471   $198.55   $198.55   $198.50  
  Purchase #6 $58.74   12.431%   $66.042   $66.04   $66.05   $66.00  
  Purchase #7 $161.72   5.745%   $171.0108   $171.01   $171.00   $171.00  
  7 purchase totals = $1,231.90       $1,347.1410   $1,347.14   $1,347.15   $1,346.90