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 $87.99   6.812%   $93.9839   $93.98   $94.00   $94.00  
  Purchase #2 $184.72   12.625%   $208.0409   $208.04   $208.05   $208.00  
  Purchase #3 $119.46   12.859%   $134.8214   $134.82   $134.80   $134.80  
  Purchase #4 $113.90   4.125%   $118.5984   $118.60   $118.60   $118.60  
  Purchase #5 $191.88   3.379%   $198.3636   $198.36   $198.35   $198.40  
  Purchase #6 $166.25   5.630%   $175.6099   $175.61   $175.60   $175.60  
  Purchase #7 $84.50   3.610%   $87.5505   $87.55   $87.55   $87.60  
  7 purchase totals = $948.70       $1,016.9686   $1,016.96   $1,016.95   $1,017.00