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 $130.71   10.662%   $144.6463   $144.65   $144.65   $144.60  
  Purchase #2 $51.99   8.233%   $56.2703   $56.27   $56.25   $56.30  
  Purchase #3 $118.51   13.482%   $134.4875   $134.49   $134.50   $134.50  
  Purchase #4 $44.95   10.833%   $49.8194   $49.82   $49.80   $49.80  
  Purchase #5 $174.78   13.304%   $198.0327   $198.03   $198.05   $198.00  
  Purchase #6 $100.31   13.353%   $113.7044   $113.70   $113.70   $113.70  
  Purchase #7 $97.67   6.558%   $104.0752   $104.08   $104.10   $104.10  
  7 purchase totals = $718.92       $801.0358   $801.04   $801.05   $801.00