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 $57.76   12.618%   $65.0482   $65.05   $65.05   $65.00  
  Purchase #2 $90.32   9.379%   $98.7911   $98.79   $98.80   $98.80  
  Purchase #3 $68.60   8.204%   $74.2279   $74.23   $74.25   $74.20  
  Purchase #4 $167.37   6.816%   $178.7779   $178.78   $178.80   $178.80  
  Purchase #5 $67.72   11.469%   $75.4868   $75.49   $75.50   $75.50  
  Purchase #6 $95.80   7.776%   $103.2494   $103.25   $103.25   $103.20  
  Purchase #7 $225.92   11.724%   $252.4069   $252.41   $252.40   $252.40  
  7 purchase totals = $773.49       $847.9882   $848.00   $848.05   $847.90