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 $235.73   11.365%   $262.5207   $262.52   $262.50   $262.50  
  Purchase #2 $131.86   10.341%   $145.4956   $145.50   $145.50   $145.50  
  Purchase #3 $76.37   6.431%   $81.2814   $81.28   $81.30   $81.30  
  Purchase #4 $250.64   6.714%   $267.468   $267.47   $267.45   $267.50  
  Purchase #5 $84.66   12.202%   $94.9902   $94.99   $95.00   $95.00  
  Purchase #6 $21.70   8.464%   $23.5367   $23.54   $23.55   $23.50  
  Purchase #7 $160.95   9.625%   $176.4414   $176.44   $176.45   $176.40  
  7 purchase totals = $961.91       $1,051.7340   $1,051.74   $1,051.75   $1,051.70