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 $58.78   13.174%   $66.5237   $66.52   $66.50   $66.50  
  Purchase #2 $61.46   8.848%   $66.898   $66.90   $66.90   $66.90  
  Purchase #3 $163.48   5.513%   $172.4927   $172.49   $172.50   $172.50  
  Purchase #4 $16.42   3.762%   $17.0377   $17.04   $17.05   $17.00  
  Purchase #5 $76.84   11.854%   $85.9486   $85.95   $85.95   $85.90  
  Purchase #6 $171.68   7.570%   $184.6762   $184.68   $184.70   $184.70  
  Purchase #7 $183.89   9.665%   $201.663   $201.66   $201.65   $201.70  
  7 purchase totals = $732.55       $795.2399   $795.24   $795.25   $795.20