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 $248.42   11.763%   $277.6416   $277.64   $277.65   $277.60  
  Purchase #2 $216.62   12.478%   $243.6498   $243.65   $243.65   $243.60  
  Purchase #3 $141.79   6.724%   $151.324   $151.32   $151.30   $151.30  
  Purchase #4 $212.73   6.247%   $226.0192   $226.02   $226.00   $226.00  
  Purchase #5 $123.77   11.204%   $137.6372   $137.64   $137.65   $137.60  
  Purchase #6 $142.55   3.604%   $147.6875   $147.69   $147.70   $147.70  
  Purchase #7 $247.60   6.461%   $263.5974   $263.60   $263.60   $263.60  
  7 purchase totals = $1,333.48       $1,447.5567   $1,447.56   $1,447.55   $1,447.40