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 $55.91   9.163%   $61.033   $61.03   $61.05   $61.00  
  Purchase #2 $224.29   11.802%   $250.7607   $250.76   $250.75   $250.80  
  Purchase #3 $8.37   8.424%   $9.0751   $9.08   $9.10   $9.10  
  Purchase #4 $26.66   4.423%   $27.8392   $27.84   $27.85   $27.80  
  Purchase #5 $5.29   7.562%   $5.69   $5.69   $5.70   $5.70  
  Purchase #6 $136.26   8.553%   $147.9143   $147.91   $147.90   $147.90  
  Purchase #7 $160.39   10.669%   $177.502   $177.50   $177.50   $177.50  
  7 purchase totals = $617.17       $679.8143   $679.81   $679.85   $679.80