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 $182.46   5.169%   $191.8914   $191.89   $191.90   $191.90  
  Purchase #2 $41.59   6.580%   $44.3266   $44.33   $44.35   $44.30  
  Purchase #3 $49.27   11.143%   $54.7602   $54.76   $54.75   $54.80  
  Purchase #4 $87.26   10.541%   $96.4581   $96.46   $96.45   $96.50  
  Purchase #5 $240.52   8.789%   $261.6593   $261.66   $261.65   $261.70  
  Purchase #6 $67.48   11.234%   $75.0607   $75.06   $75.05   $75.10  
  Purchase #7 $127.54   3.638%   $132.1799   $132.18   $132.20   $132.20  
  7 purchase totals = $796.12       $856.3362   $856.34   $856.35   $856.50