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 $24.73   5.254%   $26.0293   $26.03   $26.05   $26.00  
  Purchase #2 $227.33   8.615%   $246.9145   $246.91   $246.90   $246.90  
  Purchase #3 $49.76   10.487%   $54.9783   $54.98   $55.00   $55.00  
  Purchase #4 $139.69   12.550%   $157.2211   $157.22   $157.20   $157.20  
  Purchase #5 $107.49   7.831%   $115.9075   $115.91   $115.90   $115.90  
  Purchase #6 $181.43   6.732%   $193.6439   $193.64   $193.65   $193.60  
  Purchase #7 $191.25   6.639%   $203.9471   $203.95   $203.95   $203.90  
  7 purchase totals = $921.68       $998.6417   $998.64   $998.65   $998.50