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 $208.76   13.410%   $236.7547   $236.75   $236.75   $236.80  
  Purchase #2 $85.91   4.484%   $89.7622   $89.76   $89.75   $89.80  
  Purchase #3 $134.96   4.860%   $141.5191   $141.52   $141.50   $141.50  
  Purchase #4 $205.98   10.134%   $226.854   $226.85   $226.85   $226.90  
  Purchase #5 $232.60   6.831%   $248.4889   $248.49   $248.50   $248.50  
  Purchase #6 $144.76   7.835%   $156.1019   $156.10   $156.10   $156.10  
  Purchase #7 $7.57   5.222%   $7.9653   $7.97   $7.95   $8.00  
  7 purchase totals = $1,020.54       $1,107.4461   $1,107.44   $1,107.40   $1,107.60