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 $201.87   11.272%   $224.6248   $224.62   $224.60   $224.60  
  Purchase #2 $74.70   10.855%   $82.8087   $82.81   $82.80   $82.80  
  Purchase #3 $209.75   11.688%   $234.2656   $234.27   $234.25   $234.30  
  Purchase #4 $55.91   3.365%   $57.7914   $57.79   $57.80   $57.80  
  Purchase #5 $52.41   12.598%   $59.0126   $59.01   $59.00   $59.00  
  Purchase #6 $86.75   6.294%   $92.21   $92.21   $92.20   $92.20  
  Purchase #7 $86.56   12.674%   $97.5306   $97.53   $97.55   $97.50  
  7 purchase totals = $767.95       $848.2437   $848.24   $848.20   $848.20