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 $59.67   5.780%   $63.1189   $63.12   $63.10   $63.10  
  Purchase #2 $229.56   7.354%   $246.4418   $246.44   $246.45   $246.40  
  Purchase #3 $62.72   13.110%   $70.9426   $70.94   $70.95   $70.90  
  Purchase #4 $204.92   10.416%   $226.2645   $226.26   $226.25   $226.30  
  Purchase #5 $22.33   5.451%   $23.5472   $23.55   $23.55   $23.50  
  Purchase #6 $32.72   6.242%   $34.7624   $34.76   $34.75   $34.80  
  Purchase #7 $154.67   5.866%   $163.7429   $163.74   $163.75   $163.70  
  7 purchase totals = $766.59       $828.8203   $828.81   $828.80   $828.70