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 $223.83   10.484%   $247.2963   $247.30   $247.30   $247.30  
  Purchase #2 $118.37   13.764%   $134.6624   $134.66   $134.65   $134.70  
  Purchase #3 $69.68   5.808%   $73.727   $73.73   $73.75   $73.70  
  Purchase #4 $169.55   6.406%   $180.4114   $180.41   $180.40   $180.40  
  Purchase #5 $55.41   5.422%   $58.4143   $58.41   $58.40   $58.40  
  Purchase #6 $235.61   5.261%   $248.0054   $248.01   $248.00   $248.00  
  Purchase #7 $177.35   3.433%   $183.4384   $183.44   $183.45   $183.40  
  7 purchase totals = $1,049.80       $1,125.9552   $1,125.96   $1,125.95   $1,125.90