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 $30.94   4.271%   $32.2614   $32.26   $32.25   $32.30  
  Purchase #2 $106.74   12.335%   $119.9064   $119.91   $119.90   $119.90  
  Purchase #3 $111.82   8.412%   $121.2263   $121.23   $121.25   $121.20  
  Purchase #4 $138.80   7.542%   $149.2683   $149.27   $149.25   $149.30  
  Purchase #5 $235.51   3.616%   $244.026   $244.03   $244.05   $244.00  
  Purchase #6 $152.43   9.568%   $167.0145   $167.01   $167.00   $167.00  
  Purchase #7 $60.82   7.326%   $65.2757   $65.28   $65.30   $65.30  
  7 purchase totals = $837.06       $898.9786   $898.99   $899.00   $899.00