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 $24.34   3.306%   $25.1447   $25.14   $25.15   $25.10  
  Purchase #2 $116.76   6.368%   $124.1953   $124.20   $124.20   $124.20  
  Purchase #3 $96.32   11.800%   $107.6858   $107.69   $107.70   $107.70  
  Purchase #4 $50.32   12.709%   $56.7152   $56.72   $56.70   $56.70  
  Purchase #5 $161.58   3.493%   $167.224   $167.22   $167.20   $167.20  
  Purchase #6 $119.26   7.610%   $128.3357   $128.34   $128.35   $128.30  
  Purchase #7 $191.86   8.373%   $207.9244   $207.92   $207.90   $207.90  
  7 purchase totals = $760.44       $817.2251   $817.23   $817.20   $817.10