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 $89.71   5.874%   $94.9796   $94.98   $95.00   $95.00  
  Purchase #2 $11.35   12.522%   $12.7712   $12.77   $12.75   $12.80  
  Purchase #3 $144.94   8.711%   $157.5657   $157.57   $157.55   $157.60  
  Purchase #4 $33.64   11.703%   $37.5769   $37.58   $37.60   $37.60  
  Purchase #5 $168.31   7.857%   $181.5341   $181.53   $181.55   $181.50  
  Purchase #6 $191.87   8.718%   $208.5972   $208.60   $208.60   $208.60  
  Purchase #7 $234.53   13.428%   $266.0227   $266.02   $266.00   $266.00  
  7 purchase totals = $874.35       $959.0474   $959.05   $959.05   $959.10