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 $222.61   7.342%   $238.954   $238.95   $238.95   $239.00  
  Purchase #2 $95.42   6.570%   $101.6891   $101.69   $101.70   $101.70  
  Purchase #3 $55.75   3.273%   $57.5747   $57.57   $57.55   $57.60  
  Purchase #4 $246.39   4.607%   $257.7412   $257.74   $257.75   $257.70  
  Purchase #5 $107.91   6.742%   $115.1853   $115.19   $115.20   $115.20  
  Purchase #6 $138.46   11.568%   $154.4771   $154.48   $154.50   $154.50  
  Purchase #7 $66.52   6.365%   $70.754   $70.75   $70.75   $70.80  
  7 purchase totals = $933.06       $996.3754   $996.37   $996.40   $996.50