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 $61.71   9.464%   $67.5502   $67.55   $67.55   $67.60  
  Purchase #2 $40.34   11.251%   $44.8787   $44.88   $44.90   $44.90  
  Purchase #3 $247.35   8.645%   $268.7334   $268.73   $268.75   $268.70  
  Purchase #4 $178.65   6.748%   $190.7053   $190.71   $190.70   $190.70  
  Purchase #5 $79.68   10.326%   $87.9078   $87.91   $87.90   $87.90  
  Purchase #6 $165.70   9.789%   $181.9204   $181.92   $181.90   $181.90  
  Purchase #7 $52.91   5.684%   $55.9174   $55.92   $55.90   $55.90  
  7 purchase totals = $826.34       $897.6132   $897.62   $897.60   $897.60