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 $17.95   8.537%   $19.4824   $19.48   $19.50   $19.50  
  Purchase #2 $86.71   13.718%   $98.6049   $98.60   $98.60   $98.60  
  Purchase #3 $108.86   8.432%   $118.0391   $118.04   $118.05   $118.00  
  Purchase #4 $187.82   11.178%   $208.8145   $208.81   $208.80   $208.80  
  Purchase #5 $33.39   6.376%   $35.5189   $35.52   $35.50   $35.50  
  Purchase #6 $236.25   13.421%   $267.9571   $267.96   $267.95   $268.00  
  Purchase #7 $120.28   4.852%   $126.116   $126.12   $126.10   $126.10  
  7 purchase totals = $791.26       $874.5329   $874.53   $874.50   $874.50