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 $192.92   6.122%   $204.7306   $204.73   $204.75   $204.70  
  Purchase #2 $236.69   6.736%   $252.6334   $252.63   $252.65   $252.60  
  Purchase #3 $40.67   3.633%   $42.1475   $42.15   $42.15   $42.10  
  Purchase #4 $42.74   7.663%   $46.0152   $46.02   $46.00   $46.00  
  Purchase #5 $183.37   7.459%   $197.0476   $197.05   $197.05   $197.00  
  Purchase #6 $92.40   6.651%   $98.5455   $98.55   $98.55   $98.50  
  Purchase #7 $116.29   8.615%   $126.3084   $126.31   $126.30   $126.30  
  7 purchase totals = $905.08       $967.4282   $967.44   $967.45   $967.20