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 $61.79   10.521%   $68.2909   $68.29   $68.30   $68.30  
  Purchase #2 $240.52   4.437%   $251.1919   $251.19   $251.20   $251.20  
  Purchase #3 $105.38   11.858%   $117.876   $117.88   $117.90   $117.90  
  Purchase #4 $179.36   3.146%   $185.0027   $185.00   $185.00   $185.00  
  Purchase #5 $70.55   13.185%   $79.852   $79.85   $79.85   $79.90  
  Purchase #6 $215.98   4.818%   $226.3859   $226.39   $226.40   $226.40  
  Purchase #7 $73.58   5.811%   $77.8557   $77.86   $77.85   $77.90  
  7 purchase totals = $947.16       $1,006.4551   $1,006.46   $1,006.50   $1,006.60