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 $206.64   6.737%   $220.5613   $220.56   $220.55   $220.60  
  Purchase #2 $113.55   4.471%   $118.6268   $118.63   $118.65   $118.60  
  Purchase #3 $19.39   5.295%   $20.4167   $20.42   $20.40   $20.40  
  Purchase #4 $226.91   11.674%   $253.3995   $253.40   $253.40   $253.40  
  Purchase #5 $134.77   6.770%   $143.8939   $143.89   $143.90   $143.90  
  Purchase #6 $232.80   10.617%   $257.5164   $257.52   $257.50   $257.50  
  Purchase #7 $123.82   8.776%   $134.6864   $134.69   $134.70   $134.70  
  7 purchase totals = $1,057.88       $1,149.1010   $1,149.11   $1,149.10   $1,149.10