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 $176.83   11.510%   $197.1831   $197.18   $197.20   $197.20  
  Purchase #2 $56.91   7.265%   $61.0445   $61.04   $61.05   $61.00  
  Purchase #3 $206.25   8.380%   $223.5338   $223.53   $223.55   $223.50  
  Purchase #4 $44.39   3.447%   $45.9201   $45.92   $45.90   $45.90  
  Purchase #5 $208.67   11.140%   $231.9158   $231.92   $231.90   $231.90  
  Purchase #6 $136.94   3.685%   $141.9862   $141.99   $142.00   $142.00  
  Purchase #7 $47.72   10.339%   $52.6538   $52.65   $52.65   $52.70  
  7 purchase totals = $877.71       $954.2373   $954.23   $954.25   $954.20