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 $61.76   10.555%   $68.2788   $68.28   $68.30   $68.30  
  Purchase #2 $179.31   3.140%   $184.9403   $184.94   $184.95   $184.90  
  Purchase #3 $232.48   10.858%   $257.7227   $257.72   $257.70   $257.70  
  Purchase #4 $48.95   10.768%   $54.2209   $54.22   $54.20   $54.20  
  Purchase #5 $122.31   7.350%   $131.2998   $131.30   $131.30   $131.30  
  Purchase #6 $135.26   6.845%   $144.5185   $144.52   $144.50   $144.50  
  Purchase #7 $127.49   5.532%   $134.5427   $134.54   $134.55   $134.50  
  7 purchase totals = $907.56       $975.5237   $975.52   $975.50   $975.40