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 $67.77   12.274%   $76.0881   $76.09   $76.10   $76.10  
  Purchase #2 $204.36   9.846%   $224.4813   $224.48   $224.50   $224.50  
  Purchase #3 $105.43   11.362%   $117.409   $117.41   $117.40   $117.40  
  Purchase #4 $50.83   3.111%   $52.4113   $52.41   $52.40   $52.40  
  Purchase #5 $73.65   8.151%   $79.6532   $79.65   $79.65   $79.70  
  Purchase #6 $228.49   4.745%   $239.3319   $239.33   $239.35   $239.30  
  Purchase #7 $208.31   7.839%   $224.6394   $224.64   $224.65   $224.60  
  7 purchase totals = $938.84       $1,014.0142   $1,014.01   $1,014.05   $1,014.00