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 $222.48   8.616%   $241.6489   $241.65   $241.65   $241.60  
  Purchase #2 $222.94   7.382%   $239.3974   $239.40   $239.40   $239.40  
  Purchase #3 $222.40   8.769%   $241.9023   $241.90   $241.90   $241.90  
  Purchase #4 $186.33   13.509%   $211.5013   $211.50   $211.50   $211.50  
  Purchase #5 $232.59   4.740%   $243.6148   $243.61   $243.60   $243.60  
  Purchase #6 $211.31   3.430%   $218.5579   $218.56   $218.55   $218.60  
  Purchase #7 $236.86   6.740%   $252.8244   $252.82   $252.80   $252.80  
  7 purchase totals = $1,534.91       $1,649.4470   $1,649.44   $1,649.40   $1,649.40