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 $248.75   9.214%   $271.6698   $271.67   $271.65   $271.70  
  Purchase #2 $91.31   6.234%   $97.0023   $97.00   $97.00   $97.00  
  Purchase #3 $214.32   3.539%   $221.9048   $221.90   $221.90   $221.90  
  Purchase #4 $31.55   12.670%   $35.5474   $35.55   $35.55   $35.50  
  Purchase #5 $246.71   7.405%   $264.9789   $264.98   $265.00   $265.00  
  Purchase #6 $173.67   11.588%   $193.7949   $193.79   $193.80   $193.80  
  Purchase #7 $7.99   8.422%   $8.6629   $8.66   $8.65   $8.70  
  7 purchase totals = $1,014.30       $1,093.5610   $1,093.55   $1,093.55   $1,093.60