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 $213.97   11.118%   $237.7592   $237.76   $237.75   $237.80  
  Purchase #2 $113.26   4.366%   $118.2049   $118.20   $118.20   $118.20  
  Purchase #3 $108.48   12.515%   $122.0563   $122.06   $122.05   $122.10  
  Purchase #4 $106.71   5.357%   $112.4265   $112.43   $112.45   $112.40  
  Purchase #5 $173.70   7.323%   $186.4201   $186.42   $186.40   $186.40  
  Purchase #6 $203.76   7.741%   $219.5331   $219.53   $219.55   $219.50  
  Purchase #7 $233.72   8.159%   $252.7892   $252.79   $252.80   $252.80  
  7 purchase totals = $1,153.60       $1,249.1893   $1,249.19   $1,249.20   $1,249.20