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 $61.52   7.714%   $66.2657   $66.27   $66.25   $66.30  
  Purchase #2 $129.76   8.432%   $140.7014   $140.70   $140.70   $140.70  
  Purchase #3 $215.70   10.382%   $238.094   $238.09   $238.10   $238.10  
  Purchase #4 $44.61   7.604%   $48.0021   $48.00   $48.00   $48.00  
  Purchase #5 $225.52   9.369%   $246.649   $246.65   $246.65   $246.60  
  Purchase #6 $15.74   7.137%   $16.8634   $16.86   $16.85   $16.90  
  Purchase #7 $177.60   7.866%   $191.57   $191.57   $191.55   $191.60  
  7 purchase totals = $870.45       $948.1456   $948.14   $948.10   $948.20