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 $124.68   7.658%   $134.228   $134.23   $134.25   $134.20  
  Purchase #2 $64.83   10.677%   $71.7519   $71.75   $71.75   $71.80  
  Purchase #3 $128.26   13.517%   $145.5969   $145.60   $145.60   $145.60  
  Purchase #4 $216.45   8.353%   $234.5301   $234.53   $234.55   $234.50  
  Purchase #5 $243.26   13.430%   $275.9298   $275.93   $275.95   $275.90  
  Purchase #6 $86.44   13.638%   $98.2287   $98.23   $98.25   $98.20  
  Purchase #7 $49.41   11.500%   $55.0922   $55.09   $55.10   $55.10  
  7 purchase totals = $913.33       $1,015.3576   $1,015.36   $1,015.45   $1,015.30