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 $52.89   13.687%   $60.1291   $60.13   $60.15   $60.10  
  Purchase #2 $184.93   11.683%   $206.5354   $206.54   $206.55   $206.50  
  Purchase #3 $69.41   6.732%   $74.0827   $74.08   $74.10   $74.10  
  Purchase #4 $217.36   4.238%   $226.5717   $226.57   $226.55   $226.60  
  Purchase #5 $90.57   6.619%   $96.5648   $96.56   $96.55   $96.60  
  Purchase #6 $158.99   11.588%   $177.4138   $177.41   $177.40   $177.40  
  Purchase #7 $148.98   4.215%   $155.2595   $155.26   $155.25   $155.30  
  7 purchase totals = $923.13       $996.5570   $996.55   $996.55   $996.60