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 $54.56   13.609%   $61.9851   $61.99   $62.00   $62.00  
  Purchase #2 $103.37   4.361%   $107.878   $107.88   $107.90   $107.90  
  Purchase #3 $49.61   6.744%   $52.9557   $52.96   $52.95   $53.00  
  Purchase #4 $77.76   8.849%   $84.641   $84.64   $84.65   $84.60  
  Purchase #5 $34.42   5.439%   $36.2921   $36.29   $36.30   $36.30  
  Purchase #6 $111.37   9.243%   $121.6639   $121.66   $121.65   $121.70  
  Purchase #7 $225.73   7.130%   $241.8245   $241.82   $241.80   $241.80  
  7 purchase totals = $656.82       $707.2403   $707.24   $707.25   $707.30