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 $235.85   8.758%   $256.5057   $256.51   $256.50   $256.50  
  Purchase #2 $60.51   3.839%   $62.833   $62.83   $62.85   $62.80  
  Purchase #3 $107.33   8.794%   $116.7686   $116.77   $116.75   $116.80  
  Purchase #4 $233.30   11.743%   $260.6964   $260.70   $260.70   $260.70  
  Purchase #5 $121.64   6.573%   $129.6354   $129.64   $129.65   $129.60  
  Purchase #6 $215.57   8.696%   $234.316   $234.32   $234.30   $234.30  
  Purchase #7 $57.44   7.609%   $61.8106   $61.81   $61.80   $61.80  
  7 purchase totals = $1,031.64       $1,122.5657   $1,122.58   $1,122.55   $1,122.50