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 $64.89   8.611%   $70.4777   $70.48   $70.50   $70.50  
  Purchase #2 $202.32   4.358%   $211.1371   $211.14   $211.15   $211.10  
  Purchase #3 $135.54   9.855%   $148.8975   $148.90   $148.90   $148.90  
  Purchase #4 $63.59   9.756%   $69.7938   $69.79   $69.80   $69.80  
  Purchase #5 $81.86   10.721%   $90.6362   $90.64   $90.65   $90.60  
  Purchase #6 $11.57   3.451%   $11.9693   $11.97   $11.95   $12.00  
  Purchase #7 $108.28   13.803%   $123.2259   $123.23   $123.25   $123.20  
  7 purchase totals = $668.05       $726.1375   $726.15   $726.20   $726.10