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 $207.27   10.305%   $228.6292   $228.63   $228.65   $228.60  
  Purchase #2 $40.72   9.834%   $44.7244   $44.72   $44.70   $44.70  
  Purchase #3 $231.48   6.474%   $246.466   $246.47   $246.45   $246.50  
  Purchase #4 $30.26   6.246%   $32.15   $32.15   $32.15   $32.20  
  Purchase #5 $233.25   9.188%   $254.681   $254.68   $254.70   $254.70  
  Purchase #6 $129.82   5.788%   $137.334   $137.33   $137.35   $137.30  
  Purchase #7 $86.36   5.283%   $90.9224   $90.92   $90.90   $90.90  
  7 purchase totals = $959.16       $1,034.9070   $1,034.90   $1,034.90   $1,034.90