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 $237.25   13.721%   $269.8031   $269.80   $269.80   $269.80  
  Purchase #2 $237.93   6.449%   $253.2741   $253.27   $253.25   $253.30  
  Purchase #3 $44.68   5.330%   $47.0614   $47.06   $47.05   $47.10  
  Purchase #4 $60.33   10.506%   $66.6683   $66.67   $66.65   $66.70  
  Purchase #5 $61.54   3.383%   $63.6219   $63.62   $63.60   $63.60  
  Purchase #6 $5.65   10.841%   $6.2625   $6.26   $6.25   $6.30  
  Purchase #7 $241.58   11.231%   $268.7118   $268.71   $268.70   $268.70  
  7 purchase totals = $888.96       $975.4031   $975.39   $975.30   $975.50