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 $185.81   13.191%   $210.3202   $210.32   $210.30   $210.30  
  Purchase #2 $243.47   3.617%   $252.2763   $252.28   $252.30   $252.30  
  Purchase #3 $185.61   5.574%   $195.9559   $195.96   $195.95   $196.00  
  Purchase #4 $170.30   9.542%   $186.55   $186.55   $186.55   $186.60  
  Purchase #5 $129.86   6.320%   $138.0672   $138.07   $138.05   $138.10  
  Purchase #6 $7.88   8.305%   $8.5344   $8.53   $8.55   $8.50  
  Purchase #7 $130.46   11.451%   $145.399   $145.40   $145.40   $145.40  
  7 purchase totals = $1,053.39       $1,137.1030   $1,137.11   $1,137.10   $1,137.20