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 $47.41   5.118%   $49.8364   $49.84   $49.85   $49.80  
  Purchase #2 $232.95   12.841%   $262.8631   $262.86   $262.85   $262.90  
  Purchase #3 $177.44   10.681%   $196.3924   $196.39   $196.40   $196.40  
  Purchase #4 $171.36   5.734%   $181.1858   $181.19   $181.20   $181.20  
  Purchase #5 $93.49   10.123%   $102.954   $102.95   $102.95   $103.00  
  Purchase #6 $25.76   12.451%   $28.9674   $28.97   $28.95   $29.00  
  Purchase #7 $57.41   13.249%   $65.0163   $65.02   $65.00   $65.00  
  7 purchase totals = $805.82       $887.2154   $887.22   $887.20   $887.30