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 $63.36   9.395%   $69.3127   $69.31   $69.30   $69.30  
  Purchase #2 $115.59   5.864%   $122.3682   $122.37   $122.35   $122.40  
  Purchase #3 $73.55   7.758%   $79.256   $79.26   $79.25   $79.30  
  Purchase #4 $215.87   10.553%   $238.6508   $238.65   $238.65   $238.70  
  Purchase #5 $90.26   5.523%   $95.2451   $95.25   $95.25   $95.20  
  Purchase #6 $11.71   10.811%   $12.976   $12.98   $13.00   $13.00  
  Purchase #7 $216.59   5.565%   $228.6432   $228.64   $228.65   $228.60  
  7 purchase totals = $786.93       $846.4520   $846.46   $846.45   $846.50