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 $57.68   8.116%   $62.3613   $62.36   $62.35   $62.40  
  Purchase #2 $128.73   8.536%   $139.7184   $139.72   $139.70   $139.70  
  Purchase #3 $160.29   3.745%   $166.2929   $166.29   $166.30   $166.30  
  Purchase #4 $227.46   8.414%   $246.5985   $246.60   $246.60   $246.60  
  Purchase #5 $208.40   10.623%   $230.5383   $230.54   $230.55   $230.50  
  Purchase #6 $218.75   11.248%   $243.355   $243.36   $243.35   $243.40  
  Purchase #7 $197.37   4.613%   $206.4747   $206.47   $206.45   $206.50  
  7 purchase totals = $1,198.68       $1,295.3391   $1,295.34   $1,295.30   $1,295.40