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 $168.41   8.639%   $182.9589   $182.96   $182.95   $183.00  
  Purchase #2 $9.94   5.193%   $10.4562   $10.46   $10.45   $10.50  
  Purchase #3 $11.94   4.835%   $12.5173   $12.52   $12.50   $12.50  
  Purchase #4 $13.44   6.593%   $14.3261   $14.33   $14.35   $14.30  
  Purchase #5 $231.99   4.489%   $242.404   $242.40   $242.40   $242.40  
  Purchase #6 $67.67   9.753%   $74.2699   $74.27   $74.25   $74.30  
  Purchase #7 $104.99   13.340%   $118.9957   $119.00   $119.00   $119.00  
  7 purchase totals = $608.38       $655.9281   $655.94   $655.90   $656.00