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 $170.96   13.495%   $194.0311   $194.03   $194.05   $194.00  
  Purchase #2 $85.29   13.294%   $96.6285   $96.63   $96.65   $96.60  
  Purchase #3 $25.96   12.711%   $29.2598   $29.26   $29.25   $29.30  
  Purchase #4 $50.83   7.311%   $54.5462   $54.55   $54.55   $54.50  
  Purchase #5 $211.75   13.484%   $240.3024   $240.30   $240.30   $240.30  
  Purchase #6 $108.78   12.254%   $122.1099   $122.11   $122.10   $122.10  
  Purchase #7 $156.90   5.295%   $165.2079   $165.21   $165.20   $165.20  
  7 purchase totals = $810.47       $902.0858   $902.09   $902.10   $902.00