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 $166.90   7.403%   $179.2556   $179.26   $179.25   $179.30  
  Purchase #2 $218.37   9.281%   $238.6369   $238.64   $238.65   $238.60  
  Purchase #3 $9.31   12.416%   $10.4659   $10.47   $10.45   $10.50  
  Purchase #4 $175.82   4.631%   $183.9622   $183.96   $183.95   $184.00  
  Purchase #5 $206.55   10.372%   $227.9734   $227.97   $227.95   $228.00  
  Purchase #6 $96.54   5.564%   $101.9115   $101.91   $101.90   $101.90  
  Purchase #7 $7.43   6.789%   $7.9344   $7.93   $7.95   $7.90  
  7 purchase totals = $880.92       $950.1399   $950.14   $950.10   $950.20