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 $31.86   10.864%   $35.3213   $35.32   $35.30   $35.30  
  Purchase #2 $127.61   6.332%   $135.6903   $135.69   $135.70   $135.70  
  Purchase #3 $123.58   8.618%   $134.2301   $134.23   $134.25   $134.20  
  Purchase #4 $120.41   5.614%   $127.1698   $127.17   $127.15   $127.20  
  Purchase #5 $85.62   9.523%   $93.7736   $93.77   $93.75   $93.80  
  Purchase #6 $168.49   3.542%   $174.4579   $174.46   $174.45   $174.50  
  Purchase #7 $237.41   11.765%   $265.3413   $265.34   $265.35   $265.30  
  7 purchase totals = $894.98       $965.9843   $965.98   $965.95   $966.00