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 $95.94   3.848%   $99.6318   $99.63   $99.65   $99.60  
  Purchase #2 $188.77   11.492%   $210.4634   $210.46   $210.45   $210.50  
  Purchase #3 $58.51   7.730%   $63.0328   $63.03   $63.05   $63.00  
  Purchase #4 $147.61   6.288%   $156.8917   $156.89   $156.90   $156.90  
  Purchase #5 $246.72   8.170%   $266.877   $266.88   $266.90   $266.90  
  Purchase #6 $101.98   3.639%   $105.6911   $105.69   $105.70   $105.70  
  Purchase #7 $127.26   4.311%   $132.7462   $132.75   $132.75   $132.70  
  7 purchase totals = $966.79       $1,035.3340   $1,035.33   $1,035.40   $1,035.30