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 $61.33   6.534%   $65.3373   $65.34   $65.35   $65.30  
  Purchase #2 $178.69   11.703%   $199.6021   $199.60   $199.60   $199.60  
  Purchase #3 $93.90   11.628%   $104.8187   $104.82   $104.80   $104.80  
  Purchase #4 $16.58   3.373%   $17.1392   $17.14   $17.15   $17.10  
  Purchase #5 $212.46   4.712%   $222.4711   $222.47   $222.45   $222.50  
  Purchase #6 $203.77   10.603%   $225.3757   $225.38   $225.40   $225.40  
  Purchase #7 $5.45   6.442%   $5.8011   $5.80   $5.80   $5.80  
  7 purchase totals = $772.18       $840.5452   $840.55   $840.55   $840.50