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 $202.84   13.145%   $229.5033   $229.50   $229.50   $229.50  
  Purchase #2 $86.57   8.165%   $93.6384   $93.64   $93.65   $93.60  
  Purchase #3 $69.94   7.841%   $75.424   $75.42   $75.40   $75.40  
  Purchase #4 $90.36   9.231%   $98.7011   $98.70   $98.70   $98.70  
  Purchase #5 $165.72   3.124%   $170.8971   $170.90   $170.90   $170.90  
  Purchase #6 $37.62   9.709%   $41.2725   $41.27   $41.25   $41.30  
  Purchase #7 $186.30   11.162%   $207.0948   $207.09   $207.10   $207.10  
  7 purchase totals = $839.35       $916.5312   $916.52   $916.50   $916.50