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 $208.52   13.663%   $237.0101   $237.01   $237.00   $237.00  
  Purchase #2 $97.45   3.705%   $101.0605   $101.06   $101.05   $101.10  
  Purchase #3 $81.64   3.162%   $84.2215   $84.22   $84.20   $84.20  
  Purchase #4 $24.92   9.435%   $27.2712   $27.27   $27.25   $27.30  
  Purchase #5 $21.46   4.629%   $22.4534   $22.45   $22.45   $22.50  
  Purchase #6 $244.57   4.516%   $255.6148   $255.61   $255.60   $255.60  
  Purchase #7 $169.32   13.189%   $191.6516   $191.65   $191.65   $191.70  
  7 purchase totals = $847.88       $919.2831   $919.27   $919.20   $919.40