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 $75.86   13.715%   $86.2642   $86.26   $86.25   $86.30  
  Purchase #2 $188.28   12.400%   $211.6267   $211.63   $211.65   $211.60  
  Purchase #3 $225.83   3.415%   $233.5421   $233.54   $233.55   $233.50  
  Purchase #4 $56.68   9.291%   $61.9461   $61.95   $61.95   $61.90  
  Purchase #5 $163.65   6.323%   $173.9976   $174.00   $174.00   $174.00  
  Purchase #6 $38.77   11.461%   $43.2134   $43.21   $43.20   $43.20  
  Purchase #7 $9.62   6.420%   $10.2376   $10.24   $10.25   $10.20  
  7 purchase totals = $758.69       $820.8277   $820.83   $820.85   $820.70