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 $46.41   12.339%   $52.1365   $52.14   $52.15   $52.10  
  Purchase #2 $130.95   10.794%   $145.0847   $145.08   $145.10   $145.10  
  Purchase #3 $114.89   3.319%   $118.7032   $118.70   $118.70   $118.70  
  Purchase #4 $202.35   12.534%   $227.7125   $227.71   $227.70   $227.70  
  Purchase #5 $162.95   13.114%   $184.3193   $184.32   $184.30   $184.30  
  Purchase #6 $175.62   4.724%   $183.9163   $183.92   $183.90   $183.90  
  Purchase #7 $89.58   13.761%   $101.9071   $101.91   $101.90   $101.90  
  7 purchase totals = $922.75       $1,013.7796   $1,013.78   $1,013.75   $1,013.70