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 $214.49   10.254%   $236.4838   $236.48   $236.50   $236.50  
  Purchase #2 $132.29   3.294%   $136.6476   $136.65   $136.65   $136.60  
  Purchase #3 $181.54   3.711%   $188.2769   $188.28   $188.30   $188.30  
  Purchase #4 $81.84   8.607%   $88.884   $88.88   $88.90   $88.90  
  Purchase #5 $172.83   6.783%   $184.5531   $184.55   $184.55   $184.60  
  Purchase #6 $96.37   7.341%   $103.4445   $103.44   $103.45   $103.40  
  Purchase #7 $113.70   6.661%   $121.2736   $121.27   $121.25   $121.30  
  7 purchase totals = $993.06       $1,059.5635   $1,059.55   $1,059.60   $1,059.60