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 $243.34   10.190%   $268.1363   $268.14   $268.15   $268.10  
  Purchase #2 $208.55   8.747%   $226.7919   $226.79   $226.80   $226.80  
  Purchase #3 $168.99   9.673%   $185.3364   $185.34   $185.35   $185.30  
  Purchase #4 $59.69   13.214%   $67.5774   $67.58   $67.60   $67.60  
  Purchase #5 $16.45   9.701%   $18.0458   $18.05   $18.05   $18.00  
  Purchase #6 $6.86   3.381%   $7.0919   $7.09   $7.10   $7.10  
  Purchase #7 $169.89   11.219%   $188.95   $188.95   $188.95   $189.00  
  7 purchase totals = $873.77       $961.9297   $961.94   $962.00   $961.90