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 $77.94   4.626%   $81.5455   $81.55   $81.55   $81.50  
  Purchase #2 $159.36   10.242%   $175.6817   $175.68   $175.70   $175.70  
  Purchase #3 $108.90   5.320%   $114.6935   $114.69   $114.70   $114.70  
  Purchase #4 $172.60   8.689%   $187.5972   $187.60   $187.60   $187.60  
  Purchase #5 $184.77   12.123%   $207.1697   $207.17   $207.15   $207.20  
  Purchase #6 $179.64   9.640%   $196.9573   $196.96   $196.95   $197.00  
  Purchase #7 $56.26   7.538%   $60.5009   $60.50   $60.50   $60.50  
  7 purchase totals = $939.47       $1,024.1458   $1,024.15   $1,024.15   $1,024.20