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 $56.91   10.122%   $62.6704   $62.67   $62.65   $62.70  
  Purchase #2 $94.65   3.672%   $98.1255   $98.13   $98.15   $98.10  
  Purchase #3 $11.59   12.798%   $13.0733   $13.07   $13.05   $13.10  
  Purchase #4 $136.53   6.844%   $145.8741   $145.87   $145.85   $145.90  
  Purchase #5 $177.43   4.416%   $185.2653   $185.27   $185.25   $185.30  
  Purchase #6 $57.52   5.839%   $60.8786   $60.88   $60.90   $60.90  
  Purchase #7 $50.26   8.438%   $54.5009   $54.50   $54.50   $54.50  
  7 purchase totals = $584.89       $620.3881   $620.39   $620.35   $620.50