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 $61.34   10.173%   $67.5801   $67.58   $67.60   $67.60  
  Purchase #2 $222.61   7.301%   $238.8628   $238.86   $238.85   $238.90  
  Purchase #3 $225.64   7.764%   $243.1587   $243.16   $243.15   $243.20  
  Purchase #4 $169.73   8.650%   $184.4116   $184.41   $184.40   $184.40  
  Purchase #5 $228.62   9.432%   $250.1834   $250.18   $250.20   $250.20  
  Purchase #6 $208.54   8.543%   $226.3556   $226.36   $226.35   $226.40  
  Purchase #7 $23.84   13.642%   $27.0923   $27.09   $27.10   $27.10  
  7 purchase totals = $1,140.32       $1,237.6445   $1,237.64   $1,237.65   $1,237.80