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 $84.73   8.615%   $92.0295   $92.03   $92.05   $92.00  
  Purchase #2 $113.76   10.512%   $125.7185   $125.72   $125.70   $125.70  
  Purchase #3 $171.99   8.340%   $186.334   $186.33   $186.35   $186.30  
  Purchase #4 $136.75   11.761%   $152.8332   $152.83   $152.85   $152.80  
  Purchase #5 $73.38   13.555%   $83.3267   $83.33   $83.35   $83.30  
  Purchase #6 $135.33   6.294%   $143.8477   $143.85   $143.85   $143.80  
  Purchase #7 $190.43   13.422%   $215.9895   $215.99   $216.00   $216.00  
  7 purchase totals = $906.37       $1,000.0791   $1,000.08   $1,000.15   $999.90