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 $112.91   8.285%   $122.2646   $122.26   $122.25   $122.30  
  Purchase #2 $57.97   6.826%   $61.927   $61.93   $61.95   $61.90  
  Purchase #3 $149.84   4.403%   $156.4375   $156.44   $156.45   $156.40  
  Purchase #4 $10.52   4.652%   $11.0094   $11.01   $11.00   $11.00  
  Purchase #5 $89.90   6.495%   $95.739   $95.74   $95.75   $95.70  
  Purchase #6 $51.76   6.769%   $55.2636   $55.26   $55.25   $55.30  
  Purchase #7 $112.55   5.724%   $118.9924   $118.99   $119.00   $119.00  
  7 purchase totals = $585.45       $621.6335   $621.63   $621.65   $621.60