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 $94.29   7.621%   $101.4758   $101.48   $101.50   $101.50  
  Purchase #2 $132.33   12.460%   $148.8183   $148.82   $148.80   $148.80  
  Purchase #3 $124.33   12.447%   $139.8054   $139.81   $139.80   $139.80  
  Purchase #4 $203.93   6.550%   $217.2874   $217.29   $217.30   $217.30  
  Purchase #5 $70.72   7.509%   $76.0304   $76.03   $76.05   $76.00  
  Purchase #6 $190.80   6.252%   $202.7288   $202.73   $202.75   $202.70  
  Purchase #7 $168.43   13.581%   $191.3045   $191.30   $191.30   $191.30  
  7 purchase totals = $984.83       $1,077.4506   $1,077.46   $1,077.50   $1,077.40