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 $61.55   7.127%   $65.9367   $65.94   $65.95   $65.90  
  Purchase #2 $81.48   9.546%   $89.2581   $89.26   $89.25   $89.30  
  Purchase #3 $191.45   3.809%   $198.7423   $198.74   $198.75   $198.70  
  Purchase #4 $179.77   13.367%   $203.7999   $203.80   $203.80   $203.80  
  Purchase #5 $183.40   11.552%   $204.5864   $204.59   $204.60   $204.60  
  Purchase #6 $11.25   10.269%   $12.4053   $12.41   $12.40   $12.40  
  Purchase #7 $166.44   4.748%   $174.3426   $174.34   $174.35   $174.30  
  7 purchase totals = $875.34       $949.0713   $949.08   $949.10   $949.00