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 $211.75   12.586%   $238.4009   $238.40   $238.40   $238.40  
  Purchase #2 $63.69   5.724%   $67.3356   $67.34   $67.35   $67.30  
  Purchase #3 $172.68   3.812%   $179.2626   $179.26   $179.25   $179.30  
  Purchase #4 $72.54   7.424%   $77.9254   $77.93   $77.95   $77.90  
  Purchase #5 $150.90   5.751%   $159.5783   $159.58   $159.60   $159.60  
  Purchase #6 $199.46   11.795%   $222.9863   $222.99   $223.00   $223.00  
  Purchase #7 $86.47   10.720%   $95.7396   $95.74   $95.75   $95.70  
  7 purchase totals = $957.49       $1,041.2287   $1,041.24   $1,041.30   $1,041.20