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 $96.43   8.552%   $104.6767   $104.68   $104.70   $104.70  
  Purchase #2 $236.40   12.158%   $265.1415   $265.14   $265.15   $265.10  
  Purchase #3 $111.50   3.795%   $115.7314   $115.73   $115.75   $115.70  
  Purchase #4 $234.66   7.442%   $252.1234   $252.12   $252.10   $252.10  
  Purchase #5 $92.89   3.644%   $96.2749   $96.27   $96.25   $96.30  
  Purchase #6 $186.97   8.694%   $203.2252   $203.23   $203.25   $203.20  
  Purchase #7 $205.59   10.192%   $226.5437   $226.54   $226.55   $226.50  
  7 purchase totals = $1,164.44       $1,263.7168   $1,263.71   $1,263.75   $1,263.60