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 $157.25   6.216%   $167.0247   $167.02   $167.00   $167.00  
  Purchase #2 $192.97   6.535%   $205.5806   $205.58   $205.60   $205.60  
  Purchase #3 $227.37   3.333%   $234.9482   $234.95   $234.95   $234.90  
  Purchase #4 $81.34   12.607%   $91.5945   $91.59   $91.60   $91.60  
  Purchase #5 $116.60   13.121%   $131.8991   $131.90   $131.90   $131.90  
  Purchase #6 $231.43   6.319%   $246.0541   $246.05   $246.05   $246.10  
  Purchase #7 $99.44   3.486%   $102.9065   $102.91   $102.90   $102.90  
  7 purchase totals = $1,106.40       $1,180.0077   $1,180.00   $1,180.00   $1,180.00