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 $102.34   11.350%   $113.9556   $113.96   $113.95   $114.00  
  Purchase #2 $237.53   4.771%   $248.8626   $248.86   $248.85   $248.90  
  Purchase #3 $28.53   13.815%   $32.4714   $32.47   $32.45   $32.50  
  Purchase #4 $223.73   7.386%   $240.2547   $240.25   $240.25   $240.30  
  Purchase #5 $51.36   13.572%   $58.3306   $58.33   $58.35   $58.30  
  Purchase #6 $161.93   3.661%   $167.8583   $167.86   $167.85   $167.90  
  Purchase #7 $143.73   3.176%   $148.2949   $148.29   $148.30   $148.30  
  7 purchase totals = $949.15       $1,010.0281   $1,010.02   $1,010.00   $1,010.20