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 $191.36   10.258%   $210.9897   $210.99   $211.00   $211.00  
  Purchase #2 $103.52   11.349%   $115.2685   $115.27   $115.25   $115.30  
  Purchase #3 $110.85   7.602%   $119.2768   $119.28   $119.30   $119.30  
  Purchase #4 $248.57   4.563%   $259.9122   $259.91   $259.90   $259.90  
  Purchase #5 $184.38   4.464%   $192.6107   $192.61   $192.60   $192.60  
  Purchase #6 $95.70   11.289%   $106.5036   $106.50   $106.50   $106.50  
  Purchase #7 $10.33   4.305%   $10.7747   $10.77   $10.75   $10.80  
  7 purchase totals = $944.71       $1,015.3362   $1,015.33   $1,015.30   $1,015.40