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 $68.93   10.632%   $76.2586   $76.26   $76.25   $76.30  
  Purchase #2 $123.90   10.613%   $137.0495   $137.05   $137.05   $137.00  
  Purchase #3 $160.70   12.477%   $180.7505   $180.75   $180.75   $180.80  
  Purchase #4 $157.44   12.170%   $176.6004   $176.60   $176.60   $176.60  
  Purchase #5 $177.65   5.494%   $187.4101   $187.41   $187.40   $187.40  
  Purchase #6 $39.64   8.668%   $43.076   $43.08   $43.10   $43.10  
  Purchase #7 $29.32   9.631%   $32.1438   $32.14   $32.15   $32.10  
  7 purchase totals = $757.58       $833.2889   $833.29   $833.30   $833.30