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 $162.82   4.825%   $170.6761   $170.68   $170.70   $170.70  
  Purchase #2 $41.73   11.831%   $46.6671   $46.67   $46.65   $46.70  
  Purchase #3 $32.40   7.616%   $34.8676   $34.87   $34.85   $34.90  
  Purchase #4 $202.72   12.242%   $227.537   $227.54   $227.55   $227.50  
  Purchase #5 $242.44   9.518%   $265.5154   $265.52   $265.50   $265.50  
  Purchase #6 $111.69   5.860%   $118.235   $118.24   $118.25   $118.20  
  Purchase #7 $163.50   4.165%   $170.3098   $170.31   $170.30   $170.30  
  7 purchase totals = $957.30       $1,033.8080   $1,033.83   $1,033.80   $1,033.80