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 $50.33   5.433%   $53.0644   $53.06   $53.05   $53.10  
  Purchase #2 $51.53   13.153%   $58.3077   $58.31   $58.30   $58.30  
  Purchase #3 $166.55   8.450%   $180.6235   $180.62   $180.60   $180.60  
  Purchase #4 $203.35   13.721%   $231.2517   $231.25   $231.25   $231.30  
  Purchase #5 $174.35   9.827%   $191.4834   $191.48   $191.50   $191.50  
  Purchase #6 $61.68   6.371%   $65.6096   $65.61   $65.60   $65.60  
  Purchase #7 $79.87   7.703%   $86.0224   $86.02   $86.00   $86.00  
  7 purchase totals = $787.66       $866.3627   $866.35   $866.30   $866.40