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 $192.53   11.622%   $214.9058   $214.91   $214.90   $214.90  
  Purchase #2 $127.87   5.702%   $135.1611   $135.16   $135.15   $135.20  
  Purchase #3 $57.71   6.601%   $61.5194   $61.52   $61.50   $61.50  
  Purchase #4 $212.79   8.461%   $230.7942   $230.79   $230.80   $230.80  
  Purchase #5 $78.68   12.642%   $88.6267   $88.63   $88.65   $88.60  
  Purchase #6 $178.64   3.710%   $185.2675   $185.27   $185.25   $185.30  
  Purchase #7 $230.76   4.295%   $240.6711   $240.67   $240.65   $240.70  
  7 purchase totals = $1,078.98       $1,156.9458   $1,156.95   $1,156.90   $1,157.00