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 $58.55   8.697%   $63.6421   $63.64   $63.65   $63.60  
  Purchase #2 $37.57   3.608%   $38.9255   $38.93   $38.95   $38.90  
  Purchase #3 $173.54   5.836%   $183.6678   $183.67   $183.65   $183.70  
  Purchase #4 $43.54   6.657%   $46.4385   $46.44   $46.45   $46.40  
  Purchase #5 $244.29   6.512%   $260.1982   $260.20   $260.20   $260.20  
  Purchase #6 $156.93   4.603%   $164.1535   $164.15   $164.15   $164.20  
  Purchase #7 $234.41   6.342%   $249.2763   $249.28   $249.30   $249.30  
  7 purchase totals = $948.83       $1,006.3019   $1,006.31   $1,006.35   $1,006.30