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 $75.90   10.658%   $83.9894   $83.99   $84.00   $84.00  
  Purchase #2 $112.72   8.520%   $122.3237   $122.32   $122.30   $122.30  
  Purchase #3 $92.44   4.535%   $96.6322   $96.63   $96.65   $96.60  
  Purchase #4 $231.95   3.252%   $239.493   $239.49   $239.50   $239.50  
  Purchase #5 $126.75   6.520%   $135.0141   $135.01   $135.00   $135.00  
  Purchase #6 $113.85   5.624%   $120.2529   $120.25   $120.25   $120.30  
  Purchase #7 $59.70   4.386%   $62.3184   $62.32   $62.30   $62.30  
  7 purchase totals = $813.31       $860.0237   $860.01   $860.00   $860.00