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 $213.56   7.566%   $229.7179   $229.72   $229.70   $229.70  
  Purchase #2 $54.37   9.693%   $59.6401   $59.64   $59.65   $59.60  
  Purchase #3 $224.52   10.820%   $248.8131   $248.81   $248.80   $248.80  
  Purchase #4 $165.33   7.203%   $177.2387   $177.24   $177.25   $177.20  
  Purchase #5 $199.74   4.177%   $208.0831   $208.08   $208.10   $208.10  
  Purchase #6 $123.65   9.222%   $135.053   $135.05   $135.05   $135.10  
  Purchase #7 $154.89   13.816%   $176.2896   $176.29   $176.30   $176.30  
  7 purchase totals = $1,136.06       $1,234.8355   $1,234.83   $1,234.85   $1,234.80