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 $118.46   11.632%   $132.2393   $132.24   $132.25   $132.20  
  Purchase #2 $43.77   11.840%   $48.9524   $48.95   $48.95   $49.00  
  Purchase #3 $171.95   11.824%   $192.2814   $192.28   $192.30   $192.30  
  Purchase #4 $7.68   12.200%   $8.617   $8.62   $8.60   $8.60  
  Purchase #5 $196.60   12.216%   $220.6167   $220.62   $220.60   $220.60  
  Purchase #6 $81.44   4.493%   $85.0991   $85.10   $85.10   $85.10  
  Purchase #7 $178.35   4.783%   $186.8805   $186.88   $186.90   $186.90  
  7 purchase totals = $798.25       $874.6864   $874.69   $874.70   $874.70