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 $190.62   8.348%   $206.533   $206.53   $206.55   $206.50  
  Purchase #2 $40.54   3.384%   $41.9119   $41.91   $41.90   $41.90  
  Purchase #3 $80.96   8.705%   $88.0076   $88.01   $88.00   $88.00  
  Purchase #4 $26.83   5.606%   $28.3341   $28.33   $28.35   $28.30  
  Purchase #5 $53.49   7.845%   $57.6863   $57.69   $57.70   $57.70  
  Purchase #6 $98.73   9.307%   $107.9188   $107.92   $107.90   $107.90  
  Purchase #7 $228.80   13.691%   $260.125   $260.13   $260.15   $260.10  
  7 purchase totals = $719.97       $790.5167   $790.52   $790.55   $790.40