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 $233.28   13.339%   $264.3972   $264.40   $264.40   $264.40  
  Purchase #2 $218.50   8.122%   $236.2466   $236.25   $236.25   $236.20  
  Purchase #3 $87.66   6.253%   $93.1414   $93.14   $93.15   $93.10  
  Purchase #4 $9.93   9.376%   $10.861   $10.86   $10.85   $10.90  
  Purchase #5 $211.85   6.868%   $226.3999   $226.40   $226.40   $226.40  
  Purchase #6 $178.68   11.584%   $199.3783   $199.38   $199.40   $199.40  
  Purchase #7 $216.66   6.633%   $231.0311   $231.03   $231.05   $231.00  
  7 purchase totals = $1,156.56       $1,261.4555   $1,261.46   $1,261.50   $1,261.40