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 $246.69   7.427%   $265.0117   $265.01   $265.00   $265.00  
  Purchase #2 $55.58   11.527%   $61.9867   $61.99   $62.00   $62.00  
  Purchase #3 $176.29   7.434%   $189.3954   $189.40   $189.40   $189.40  
  Purchase #4 $42.57   10.601%   $47.0828   $47.08   $47.10   $47.10  
  Purchase #5 $60.74   5.165%   $63.8772   $63.88   $63.90   $63.90  
  Purchase #6 $180.26   3.160%   $185.9562   $185.96   $185.95   $186.00  
  Purchase #7 $81.60   13.558%   $92.6633   $92.66   $92.65   $92.70  
  7 purchase totals = $843.73       $905.9733   $905.98   $906.00   $906.10