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 $241.79   11.501%   $269.5983   $269.60   $269.60   $269.60  
  Purchase #2 $44.54   13.291%   $50.4598   $50.46   $50.45   $50.50  
  Purchase #3 $244.58   13.174%   $276.801   $276.80   $276.80   $276.80  
  Purchase #4 $183.40   12.119%   $205.6262   $205.63   $205.65   $205.60  
  Purchase #5 $29.50   3.788%   $30.6175   $30.62   $30.60   $30.60  
  Purchase #6 $41.65   12.575%   $46.8875   $46.89   $46.90   $46.90  
  Purchase #7 $225.29   13.349%   $255.364   $255.36   $255.35   $255.40  
  7 purchase totals = $1,010.75       $1,135.3543   $1,135.36   $1,135.35   $1,135.40