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 $62.58   13.368%   $70.9457   $70.95   $70.95   $70.90  
  Purchase #2 $57.93   5.111%   $60.8908   $60.89   $60.90   $60.90  
  Purchase #3 $151.40   10.630%   $167.4938   $167.49   $167.50   $167.50  
  Purchase #4 $237.88   13.200%   $269.2802   $269.28   $269.30   $269.30  
  Purchase #5 $56.32   12.105%   $63.1375   $63.14   $63.15   $63.10  
  Purchase #6 $232.50   7.860%   $250.7745   $250.77   $250.75   $250.80  
  Purchase #7 $191.80   5.662%   $202.6597   $202.66   $202.65   $202.70  
  7 purchase totals = $990.41       $1,085.1822   $1,085.18   $1,085.20   $1,085.20