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 $60.52   4.494%   $63.2398   $63.24   $63.25   $63.20  
  Purchase #2 $185.42   11.864%   $207.4182   $207.42   $207.40   $207.40  
  Purchase #3 $147.92   6.775%   $157.9416   $157.94   $157.95   $157.90  
  Purchase #4 $211.67   4.623%   $221.4555   $221.46   $221.45   $221.50  
  Purchase #5 $20.79   7.351%   $22.3183   $22.32   $22.30   $22.30  
  Purchase #6 $30.73   8.767%   $33.4241   $33.42   $33.40   $33.40  
  Purchase #7 $86.33   4.611%   $90.3107   $90.31   $90.30   $90.30  
  7 purchase totals = $743.38       $796.1082   $796.11   $796.05   $796.00