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 $62.92   5.817%   $66.5801   $66.58   $66.60   $66.60  
  Purchase #2 $238.25   12.780%   $268.6984   $268.70   $268.70   $268.70  
  Purchase #3 $208.44   10.286%   $229.8801   $229.88   $229.90   $229.90  
  Purchase #4 $73.92   3.820%   $76.7437   $76.74   $76.75   $76.70  
  Purchase #5 $151.67   3.462%   $156.9208   $156.92   $156.90   $156.90  
  Purchase #6 $196.93   5.247%   $207.2629   $207.26   $207.25   $207.30  
  Purchase #7 $193.69   13.450%   $219.7413   $219.74   $219.75   $219.70  
  7 purchase totals = $1,125.82       $1,225.8273   $1,225.82   $1,225.85   $1,225.80