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 $57.94   6.414%   $61.6563   $61.66   $61.65   $61.70  
  Purchase #2 $159.33   11.685%   $177.9477   $177.95   $177.95   $177.90  
  Purchase #3 $201.93   6.417%   $214.8878   $214.89   $214.90   $214.90  
  Purchase #4 $41.66   7.170%   $44.647   $44.65   $44.65   $44.60  
  Purchase #5 $186.83   13.435%   $211.9306   $211.93   $211.95   $211.90  
  Purchase #6 $63.37   6.262%   $67.3382   $67.34   $67.35   $67.30  
  Purchase #7 $134.87   6.744%   $143.9656   $143.97   $143.95   $144.00  
  7 purchase totals = $845.93       $922.3732   $922.39   $922.40   $922.30