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 $15.33   4.514%   $16.022   $16.02   $16.00   $16.00  
  Purchase #2 $164.80   4.159%   $171.654   $171.65   $171.65   $171.70  
  Purchase #3 $244.26   3.793%   $253.5248   $253.52   $253.50   $253.50  
  Purchase #4 $23.96   12.466%   $26.9469   $26.95   $26.95   $26.90  
  Purchase #5 $129.94   11.750%   $145.208   $145.21   $145.20   $145.20  
  Purchase #6 $48.30   8.296%   $52.307   $52.31   $52.30   $52.30  
  Purchase #7 $176.50   13.468%   $200.271   $200.27   $200.25   $200.30  
  7 purchase totals = $803.09       $865.9337   $865.93   $865.85   $865.90