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 $168.85   10.567%   $186.6924   $186.69   $186.70   $186.70  
  Purchase #2 $220.82   11.658%   $246.5632   $246.56   $246.55   $246.60  
  Purchase #3 $131.87   3.544%   $136.5435   $136.54   $136.55   $136.50  
  Purchase #4 $137.48   5.172%   $144.5905   $144.59   $144.60   $144.60  
  Purchase #5 $49.27   5.704%   $52.0804   $52.08   $52.10   $52.10  
  Purchase #6 $15.73   11.315%   $17.5098   $17.51   $17.50   $17.50  
  Purchase #7 $203.89   3.753%   $211.542   $211.54   $211.55   $211.50  
  7 purchase totals = $927.91       $995.5218   $995.51   $995.55   $995.50