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 $207.52   13.210%   $234.9334   $234.93   $234.95   $234.90  
  Purchase #2 $238.42   13.783%   $271.2814   $271.28   $271.30   $271.30  
  Purchase #3 $168.66   10.279%   $185.9966   $186.00   $186.00   $186.00  
  Purchase #4 $176.99   4.135%   $184.3085   $184.31   $184.30   $184.30  
  Purchase #5 $150.41   3.697%   $155.9707   $155.97   $155.95   $156.00  
  Purchase #6 $76.40   12.106%   $85.649   $85.65   $85.65   $85.60  
  Purchase #7 $35.46   10.154%   $39.0606   $39.06   $39.05   $39.10  
  7 purchase totals = $1,053.86       $1,157.2002   $1,157.20   $1,157.20   $1,157.20