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 $249.58   13.246%   $282.6394   $282.64   $282.65   $282.60  
  Purchase #2 $192.80   7.130%   $206.5466   $206.55   $206.55   $206.50  
  Purchase #3 $147.54   7.126%   $158.0537   $158.05   $158.05   $158.10  
  Purchase #4 $196.50   9.416%   $215.0024   $215.00   $215.00   $215.00  
  Purchase #5 $196.51   5.285%   $206.8956   $206.90   $206.90   $206.90  
  Purchase #6 $244.82   12.551%   $275.5474   $275.55   $275.55   $275.50  
  Purchase #7 $144.68   3.832%   $150.2241   $150.22   $150.20   $150.20  
  7 purchase totals = $1,372.43       $1,494.9092   $1,494.91   $1,494.90   $1,494.80