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 $112.55   12.818%   $126.9767   $126.98   $127.00   $127.00  
  Purchase #2 $5.93   3.516%   $6.1385   $6.14   $6.15   $6.10  
  Purchase #3 $10.99   5.489%   $11.5932   $11.59   $11.60   $11.60  
  Purchase #4 $98.81   3.158%   $101.9304   $101.93   $101.95   $101.90  
  Purchase #5 $248.45   10.653%   $274.9174   $274.92   $274.90   $274.90  
  Purchase #6 $96.60   3.832%   $100.3017   $100.30   $100.30   $100.30  
  Purchase #7 $199.72   7.143%   $213.986   $213.99   $214.00   $214.00  
  7 purchase totals = $773.05       $835.8439   $835.85   $835.90   $835.80