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 $39.49   10.687%   $43.7103   $43.71   $43.70   $43.70  
  Purchase #2 $98.58   6.464%   $104.9522   $104.95   $104.95   $105.00  
  Purchase #3 $67.89   8.608%   $73.734   $73.73   $73.75   $73.70  
  Purchase #4 $211.68   9.578%   $231.9547   $231.95   $231.95   $232.00  
  Purchase #5 $144.58   10.505%   $159.7681   $159.77   $159.75   $159.80  
  Purchase #6 $55.29   4.556%   $57.809   $57.81   $57.80   $57.80  
  Purchase #7 $39.30   6.565%   $41.88   $41.88   $41.90   $41.90  
  7 purchase totals = $656.81       $713.8083   $713.80   $713.80   $713.90