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 $109.92   8.119%   $118.8444   $118.84   $118.85   $118.80  
  Purchase #2 $114.92   8.464%   $124.6468   $124.65   $124.65   $124.60  
  Purchase #3 $176.39   5.641%   $186.3402   $186.34   $186.35   $186.30  
  Purchase #4 $156.98   8.361%   $170.1051   $170.11   $170.10   $170.10  
  Purchase #5 $208.84   11.414%   $232.677   $232.68   $232.70   $232.70  
  Purchase #6 $61.71   13.136%   $69.8162   $69.82   $69.80   $69.80  
  Purchase #7 $88.78   8.229%   $96.0857   $96.09   $96.10   $96.10  
  7 purchase totals = $917.54       $998.5154   $998.53   $998.55   $998.40