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 $248.88   6.220%   $264.3603   $264.36   $264.35   $264.40  
  Purchase #2 $177.94   12.210%   $199.6665   $199.67   $199.65   $199.70  
  Purchase #3 $106.47   10.228%   $117.3598   $117.36   $117.35   $117.40  
  Purchase #4 $63.86   12.344%   $71.7429   $71.74   $71.75   $71.70  
  Purchase #5 $43.58   6.557%   $46.4375   $46.44   $46.45   $46.40  
  Purchase #6 $226.25   12.151%   $253.7416   $253.74   $253.75   $253.70  
  Purchase #7 $218.62   5.756%   $231.2038   $231.20   $231.20   $231.20  
  7 purchase totals = $1,085.60       $1,184.5124   $1,184.51   $1,184.50   $1,184.50