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 $70.50   5.668%   $74.4959   $74.50   $74.50   $74.50  
  Purchase #2 $134.92   12.624%   $151.9523   $151.95   $151.95   $152.00  
  Purchase #3 $180.28   3.421%   $186.4474   $186.45   $186.45   $186.40  
  Purchase #4 $218.53   8.165%   $236.373   $236.37   $236.35   $236.40  
  Purchase #5 $38.32   4.153%   $39.9114   $39.91   $39.90   $39.90  
  Purchase #6 $25.31   3.805%   $26.273   $26.27   $26.25   $26.30  
  Purchase #7 $32.96   3.244%   $34.0292   $34.03   $34.05   $34.00  
  7 purchase totals = $700.82       $749.4822   $749.48   $749.45   $749.50