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 $61.39   10.729%   $67.9765   $67.98   $68.00   $68.00  
  Purchase #2 $50.73   12.391%   $57.016   $57.02   $57.00   $57.00  
  Purchase #3 $247.48   7.441%   $265.895   $265.90   $265.90   $265.90  
  Purchase #4 $161.34   5.686%   $170.5138   $170.51   $170.50   $170.50  
  Purchase #5 $128.27   11.490%   $143.0082   $143.01   $143.00   $143.00  
  Purchase #6 $223.89   12.760%   $252.4584   $252.46   $252.45   $252.50  
  Purchase #7 $155.61   13.578%   $176.7387   $176.74   $176.75   $176.70  
  7 purchase totals = $1,028.71       $1,133.6066   $1,133.62   $1,133.60   $1,133.60