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 $114.32   13.104%   $129.3005   $129.30   $129.30   $129.30  
  Purchase #2 $201.26   4.322%   $209.9585   $209.96   $209.95   $210.00  
  Purchase #3 $17.68   5.459%   $18.6452   $18.65   $18.65   $18.60  
  Purchase #4 $205.48   9.747%   $225.5081   $225.51   $225.50   $225.50  
  Purchase #5 $223.45   4.372%   $233.2192   $233.22   $233.20   $233.20  
  Purchase #6 $114.28   3.643%   $118.4432   $118.44   $118.45   $118.40  
  Purchase #7 $117.72   8.262%   $127.446   $127.45   $127.45   $127.40  
  7 purchase totals = $994.19       $1,062.5207   $1,062.53   $1,062.50   $1,062.40