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 $82.65   12.749%   $93.187   $93.19   $93.20   $93.20  
  Purchase #2 $214.59   13.797%   $244.197   $244.20   $244.20   $244.20  
  Purchase #3 $5.74   13.545%   $6.5175   $6.52   $6.50   $6.50  
  Purchase #4 $99.77   13.842%   $113.5802   $113.58   $113.60   $113.60  
  Purchase #5 $45.70   11.737%   $51.0638   $51.06   $51.05   $51.10  
  Purchase #6 $227.91   9.174%   $248.8185   $248.82   $248.80   $248.80  
  Purchase #7 $127.61   3.282%   $131.7982   $131.80   $131.80   $131.80  
  7 purchase totals = $803.97       $889.1622   $889.17   $889.15   $889.20