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 $91.36   5.106%   $96.0248   $96.02   $96.00   $96.00  
  Purchase #2 $200.86   8.370%   $217.672   $217.67   $217.65   $217.70  
  Purchase #3 $61.84   6.714%   $65.9919   $65.99   $66.00   $66.00  
  Purchase #4 $59.41   3.702%   $61.6094   $61.61   $61.60   $61.60  
  Purchase #5 $131.88   3.670%   $136.72   $136.72   $136.70   $136.70  
  Purchase #6 $213.67   5.713%   $225.877   $225.88   $225.90   $225.90  
  Purchase #7 $63.54   6.768%   $67.8404   $67.84   $67.85   $67.80  
  7 purchase totals = $822.56       $871.7355   $871.73   $871.70   $871.70