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 $162.46   13.230%   $183.9535   $183.95   $183.95   $184.00  
  Purchase #2 $214.37   7.706%   $230.8894   $230.89   $230.90   $230.90  
  Purchase #3 $14.63   6.478%   $15.5777   $15.58   $15.60   $15.60  
  Purchase #4 $224.54   9.585%   $246.0622   $246.06   $246.05   $246.10  
  Purchase #5 $144.76   5.316%   $152.4554   $152.46   $152.45   $152.50  
  Purchase #6 $68.65   12.279%   $77.0795   $77.08   $77.10   $77.10  
  Purchase #7 $195.86   9.871%   $215.1933   $215.19   $215.20   $215.20  
  7 purchase totals = $1,025.27       $1,121.2110   $1,121.21   $1,121.25   $1,121.40