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 $95.47   6.643%   $101.8121   $101.81   $101.80   $101.80  
  Purchase #2 $109.80   3.360%   $113.4893   $113.49   $113.50   $113.50  
  Purchase #3 $110.77   5.524%   $116.8889   $116.89   $116.90   $116.90  
  Purchase #4 $117.82   7.851%   $127.07   $127.07   $127.05   $127.10  
  Purchase #5 $249.45   9.861%   $274.0483   $274.05   $274.05   $274.00  
  Purchase #6 $45.25   3.831%   $46.9835   $46.98   $47.00   $47.00  
  Purchase #7 $210.46   9.692%   $230.8578   $230.86   $230.85   $230.90  
  7 purchase totals = $939.02       $1,011.1499   $1,011.15   $1,011.15   $1,011.20