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 $65.36   12.797%   $73.7241   $73.72   $73.70   $73.70  
  Purchase #2 $72.62   9.365%   $79.4209   $79.42   $79.40   $79.40  
  Purchase #3 $177.95   13.127%   $201.3095   $201.31   $201.30   $201.30  
  Purchase #4 $194.77   7.253%   $208.8967   $208.90   $208.90   $208.90  
  Purchase #5 $202.69   9.621%   $222.1908   $222.19   $222.20   $222.20  
  Purchase #6 $232.63   6.523%   $247.8045   $247.80   $247.80   $247.80  
  Purchase #7 $89.80   12.161%   $100.7206   $100.72   $100.70   $100.70  
  7 purchase totals = $1,035.82       $1,134.0671   $1,134.06   $1,134.00   $1,134.00