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 $54.93   8.645%   $59.6787   $59.68   $59.70   $59.70  
  Purchase #2 $173.46   13.381%   $196.6707   $196.67   $196.65   $196.70  
  Purchase #3 $96.49   3.320%   $99.6935   $99.69   $99.70   $99.70  
  Purchase #4 $194.98   3.781%   $202.3522   $202.35   $202.35   $202.40  
  Purchase #5 $163.96   8.291%   $177.5539   $177.55   $177.55   $177.60  
  Purchase #6 $246.61   9.368%   $269.7124   $269.71   $269.70   $269.70  
  Purchase #7 $122.80   8.291%   $132.9813   $132.98   $133.00   $133.00  
  7 purchase totals = $1,053.23       $1,138.6427   $1,138.63   $1,138.65   $1,138.80