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 $228.36   10.477%   $252.2853   $252.29   $252.30   $252.30  
  Purchase #2 $164.53   3.721%   $170.6522   $170.65   $170.65   $170.70  
  Purchase #3 $20.28   10.115%   $22.3313   $22.33   $22.35   $22.30  
  Purchase #4 $61.27   13.814%   $69.7338   $69.73   $69.75   $69.70  
  Purchase #5 $227.42   7.559%   $244.6107   $244.61   $244.60   $244.60  
  Purchase #6 $49.83   13.286%   $56.4504   $56.45   $56.45   $56.50  
  Purchase #7 $188.26   9.778%   $206.6681   $206.67   $206.65   $206.70  
  7 purchase totals = $939.95       $1,022.7318   $1,022.73   $1,022.75   $1,022.80