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 $164.52   10.620%   $181.992   $181.99   $182.00   $182.00  
  Purchase #2 $65.43   6.655%   $69.7844   $69.78   $69.80   $69.80  
  Purchase #3 $13.40   8.779%   $14.5764   $14.58   $14.60   $14.60  
  Purchase #4 $142.94   8.710%   $155.3901   $155.39   $155.40   $155.40  
  Purchase #5 $231.29   7.227%   $248.0053   $248.01   $248.00   $248.00  
  Purchase #6 $8.65   6.626%   $9.2231   $9.22   $9.20   $9.20  
  Purchase #7 $47.93   13.521%   $54.4106   $54.41   $54.40   $54.40  
  7 purchase totals = $674.16       $733.3819   $733.38   $733.40   $733.40