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 $157.71   12.644%   $177.6509   $177.65   $177.65   $177.70  
  Purchase #2 $237.97   13.599%   $270.3315   $270.33   $270.35   $270.30  
  Purchase #3 $216.89   8.382%   $235.0697   $235.07   $235.05   $235.10  
  Purchase #4 $61.85   10.791%   $68.5242   $68.52   $68.50   $68.50  
  Purchase #5 $190.56   9.549%   $208.7566   $208.76   $208.75   $208.80  
  Purchase #6 $196.61   9.549%   $215.3843   $215.38   $215.40   $215.40  
  Purchase #7 $164.82   4.239%   $171.8067   $171.81   $171.80   $171.80  
  7 purchase totals = $1,226.41       $1,347.5239   $1,347.52   $1,347.50   $1,347.60