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 $64.94   4.699%   $67.9915   $67.99   $68.00   $68.00  
  Purchase #2 $215.71   11.233%   $239.9407   $239.94   $239.95   $239.90  
  Purchase #3 $61.77   11.580%   $68.923   $68.92   $68.90   $68.90  
  Purchase #4 $171.66   3.125%   $177.0244   $177.02   $177.00   $177.00  
  Purchase #5 $84.52   13.743%   $96.1356   $96.14   $96.15   $96.10  
  Purchase #6 $62.66   9.459%   $68.587   $68.59   $68.60   $68.60  
  Purchase #7 $148.87   3.340%   $153.8423   $153.84   $153.85   $153.80  
  7 purchase totals = $810.13       $872.4445   $872.44   $872.45   $872.30