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 $24.27   11.366%   $27.0285   $27.03   $27.05   $27.00  
  Purchase #2 $167.93   4.624%   $175.6951   $175.70   $175.70   $175.70  
  Purchase #3 $58.64   8.636%   $63.7042   $63.70   $63.70   $63.70  
  Purchase #4 $58.52   3.392%   $60.505   $60.51   $60.50   $60.50  
  Purchase #5 $222.87   9.258%   $243.5033   $243.50   $243.50   $243.50  
  Purchase #6 $234.72   9.548%   $257.1311   $257.13   $257.15   $257.10  
  Purchase #7 $16.56   10.188%   $18.2471   $18.25   $18.25   $18.20  
  7 purchase totals = $783.51       $845.8143   $845.82   $845.85   $845.70