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 $246.98   8.640%   $268.3191   $268.32   $268.30   $268.30  
  Purchase #2 $126.73   4.278%   $132.1515   $132.15   $132.15   $132.20  
  Purchase #3 $156.34   4.657%   $163.6208   $163.62   $163.60   $163.60  
  Purchase #4 $184.76   6.116%   $196.0599   $196.06   $196.05   $196.10  
  Purchase #5 $89.61   6.354%   $95.3038   $95.30   $95.30   $95.30  
  Purchase #6 $194.59   11.368%   $216.711   $216.71   $216.70   $216.70  
  Purchase #7 $38.60   6.805%   $41.2267   $41.23   $41.25   $41.20  
  7 purchase totals = $1,037.61       $1,113.3928   $1,113.39   $1,113.35   $1,113.40