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 $49.93   5.616%   $52.7341   $52.73   $52.75   $52.70  
  Purchase #2 $88.76   4.836%   $93.0524   $93.05   $93.05   $93.10  
  Purchase #3 $105.92   4.693%   $110.8908   $110.89   $110.90   $110.90  
  Purchase #4 $126.31   8.565%   $137.1285   $137.13   $137.15   $137.10  
  Purchase #5 $166.94   7.538%   $179.5239   $179.52   $179.50   $179.50  
  Purchase #6 $236.48   6.690%   $252.3005   $252.30   $252.30   $252.30  
  Purchase #7 $208.46   4.752%   $218.366   $218.37   $218.35   $218.40  
  7 purchase totals = $982.80       $1,043.9962   $1,043.99   $1,044.00   $1,044.00