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 $248.67   8.562%   $269.9611   $269.96   $269.95   $270.00  
  Purchase #2 $51.96   7.787%   $56.0061   $56.01   $56.00   $56.00  
  Purchase #3 $193.42   11.771%   $216.1875   $216.19   $216.20   $216.20  
  Purchase #4 $16.33   12.619%   $18.3907   $18.39   $18.40   $18.40  
  Purchase #5 $79.42   8.369%   $86.0667   $86.07   $86.05   $86.10  
  Purchase #6 $139.92   11.859%   $156.5131   $156.51   $156.50   $156.50  
  Purchase #7 $128.45   11.644%   $143.4067   $143.41   $143.40   $143.40  
  7 purchase totals = $858.17       $946.5319   $946.54   $946.50   $946.60