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 $244.34   10.230%   $269.336   $269.34   $269.35   $269.30  
  Purchase #2 $79.80   9.489%   $87.3722   $87.37   $87.35   $87.40  
  Purchase #3 $45.66   7.376%   $49.0279   $49.03   $49.05   $49.00  
  Purchase #4 $64.54   12.767%   $72.7798   $72.78   $72.80   $72.80  
  Purchase #5 $244.59   5.855%   $258.9107   $258.91   $258.90   $258.90  
  Purchase #6 $114.25   7.481%   $122.797   $122.80   $122.80   $122.80  
  Purchase #7 $33.67   8.832%   $36.6437   $36.64   $36.65   $36.60  
  7 purchase totals = $826.85       $896.8673   $896.87   $896.90   $896.80