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 $59.99   3.673%   $62.1934   $62.19   $62.20   $62.20  
  Purchase #2 $40.64   3.283%   $41.9742   $41.97   $41.95   $42.00  
  Purchase #3 $49.46   6.811%   $52.8287   $52.83   $52.85   $52.80  
  Purchase #4 $116.29   5.311%   $122.4662   $122.47   $122.45   $122.50  
  Purchase #5 $183.35   9.162%   $200.1485   $200.15   $200.15   $200.10  
  Purchase #6 $209.55   13.214%   $237.2399   $237.24   $237.25   $237.20  
  Purchase #7 $232.68   13.416%   $263.8963   $263.90   $263.90   $263.90  
  7 purchase totals = $891.96       $980.7472   $980.75   $980.75   $980.70