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 $156.48   7.337%   $167.9609   $167.96   $167.95   $168.00  
  Purchase #2 $93.45   13.763%   $106.3115   $106.31   $106.30   $106.30  
  Purchase #3 $106.66   6.822%   $113.9363   $113.94   $113.95   $113.90  
  Purchase #4 $177.26   9.147%   $193.474   $193.47   $193.45   $193.50  
  Purchase #5 $11.45   3.599%   $11.8621   $11.86   $11.85   $11.90  
  Purchase #6 $151.65   11.788%   $169.5265   $169.53   $169.55   $169.50  
  Purchase #7 $96.43   7.769%   $103.9216   $103.92   $103.90   $103.90  
  7 purchase totals = $793.38       $866.9929   $866.99   $866.95   $867.00