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 $238.45   9.564%   $261.2554   $261.26   $261.25   $261.30  
  Purchase #2 $11.55   6.710%   $12.325   $12.33   $12.35   $12.30  
  Purchase #3 $156.92   12.622%   $176.7264   $176.73   $176.75   $176.70  
  Purchase #4 $38.77   7.282%   $41.5932   $41.59   $41.60   $41.60  
  Purchase #5 $88.52   8.771%   $96.2841   $96.28   $96.30   $96.30  
  Purchase #6 $167.89   6.449%   $178.7172   $178.72   $178.70   $178.70  
  Purchase #7 $138.53   4.123%   $144.2416   $144.24   $144.25   $144.20  
  7 purchase totals = $840.63       $911.1429   $911.15   $911.20   $911.10