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 $221.59   8.575%   $240.5913   $240.59   $240.60   $240.60  
  Purchase #2 $145.68   11.741%   $162.7843   $162.78   $162.80   $162.80  
  Purchase #3 $169.38   4.806%   $177.5204   $177.52   $177.50   $177.50  
  Purchase #4 $158.48   13.295%   $179.5499   $179.55   $179.55   $179.50  
  Purchase #5 $106.36   5.555%   $112.2683   $112.27   $112.25   $112.30  
  Purchase #6 $32.59   8.545%   $35.3748   $35.37   $35.35   $35.40  
  Purchase #7 $102.98   3.134%   $106.2074   $106.21   $106.20   $106.20  
  7 purchase totals = $937.06       $1,014.2964   $1,014.29   $1,014.25   $1,014.30