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 $172.38   5.629%   $182.0833   $182.08   $182.10   $182.10  
  Purchase #2 $219.77   8.548%   $238.5559   $238.56   $238.55   $238.60  
  Purchase #3 $27.65   10.688%   $30.6052   $30.61   $30.60   $30.60  
  Purchase #4 $98.92   10.499%   $109.3056   $109.31   $109.30   $109.30  
  Purchase #5 $180.68   11.535%   $201.5214   $201.52   $201.50   $201.50  
  Purchase #6 $234.28   7.797%   $252.5468   $252.55   $252.55   $252.50  
  Purchase #7 $237.90   6.617%   $253.6418   $253.64   $253.65   $253.60  
  7 purchase totals = $1,171.58       $1,268.2600   $1,268.27   $1,268.25   $1,268.20