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 $116.91   6.529%   $124.5431   $124.54   $124.55   $124.50  
  Purchase #2 $21.96   12.479%   $24.7004   $24.70   $24.70   $24.70  
  Purchase #3 $196.94   5.153%   $207.0883   $207.09   $207.10   $207.10  
  Purchase #4 $113.34   11.663%   $126.5588   $126.56   $126.55   $126.60  
  Purchase #5 $176.63   6.384%   $187.9061   $187.91   $187.90   $187.90  
  Purchase #6 $192.95   7.483%   $207.3884   $207.39   $207.40   $207.40  
  Purchase #7 $177.33   4.219%   $184.8116   $184.81   $184.80   $184.80  
  7 purchase totals = $996.06       $1,062.9967   $1,063.00   $1,063.00   $1,063.00