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 $224.30   10.460%   $247.7618   $247.76   $247.75   $247.80  
  Purchase #2 $72.60   6.764%   $77.5107   $77.51   $77.50   $77.50  
  Purchase #3 $130.57   6.166%   $138.6209   $138.62   $138.60   $138.60  
  Purchase #4 $100.81   6.719%   $107.5834   $107.58   $107.60   $107.60  
  Purchase #5 $162.27   12.546%   $182.6284   $182.63   $182.65   $182.60  
  Purchase #6 $169.45   11.104%   $188.2657   $188.27   $188.25   $188.30  
  Purchase #7 $31.88   6.710%   $34.0191   $34.02   $34.00   $34.00  
  7 purchase totals = $891.88       $976.3900   $976.39   $976.35   $976.40