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 $225.35   11.699%   $251.7137   $251.71   $251.70   $251.70  
  Purchase #2 $172.96   11.614%   $193.0476   $193.05   $193.05   $193.00  
  Purchase #3 $185.97   12.137%   $208.5412   $208.54   $208.55   $208.50  
  Purchase #4 $55.64   7.758%   $59.9566   $59.96   $59.95   $60.00  
  Purchase #5 $166.95   12.335%   $187.5433   $187.54   $187.55   $187.50  
  Purchase #6 $100.49   12.420%   $112.9709   $112.97   $112.95   $113.00  
  Purchase #7 $234.36   8.470%   $254.2103   $254.21   $254.20   $254.20  
  7 purchase totals = $1,141.72       $1,267.9836   $1,267.98   $1,267.95   $1,267.90