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 $54.81   8.613%   $59.5308   $59.53   $59.55   $59.50  
  Purchase #2 $176.81   9.413%   $193.4531   $193.45   $193.45   $193.50  
  Purchase #3 $79.52   10.764%   $88.0795   $88.08   $88.10   $88.10  
  Purchase #4 $34.38   5.865%   $36.3964   $36.40   $36.40   $36.40  
  Purchase #5 $206.53   7.442%   $221.9   $221.90   $221.90   $221.90  
  Purchase #6 $16.61   12.800%   $18.7361   $18.74   $18.75   $18.70  
  Purchase #7 $71.45   9.161%   $77.9955   $78.00   $78.00   $78.00  
  7 purchase totals = $640.11       $696.0914   $696.10   $696.15   $696.10