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 $111.36   11.638%   $124.3201   $124.32   $124.30   $124.30  
  Purchase #2 $144.68   5.794%   $153.0628   $153.06   $153.05   $153.10  
  Purchase #3 $220.63   10.250%   $243.2446   $243.24   $243.25   $243.20  
  Purchase #4 $202.77   8.438%   $219.8797   $219.88   $219.90   $219.90  
  Purchase #5 $91.71   7.622%   $98.7001   $98.70   $98.70   $98.70  
  Purchase #6 $130.59   3.869%   $135.6425   $135.64   $135.65   $135.60  
  Purchase #7 $85.95   5.633%   $90.7916   $90.79   $90.80   $90.80  
  7 purchase totals = $987.69       $1,065.6414   $1,065.63   $1,065.65   $1,065.60