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 $64.97   4.163%   $67.6747   $67.67   $67.65   $67.70  
  Purchase #2 $200.28   9.193%   $218.6917   $218.69   $218.70   $218.70  
  Purchase #3 $208.62   8.399%   $226.142   $226.14   $226.15   $226.10  
  Purchase #4 $201.95   12.535%   $227.2644   $227.26   $227.25   $227.30  
  Purchase #5 $5.85   12.791%   $6.5983   $6.60   $6.60   $6.60  
  Purchase #6 $247.33   12.280%   $277.7021   $277.70   $277.70   $277.70  
  Purchase #7 $10.83   3.200%   $11.1766   $11.18   $11.20   $11.20  
  7 purchase totals = $939.83       $1,035.2498   $1,035.24   $1,035.25   $1,035.30