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 $248.52   11.174%   $276.2896   $276.29   $276.30   $276.30  
  Purchase #2 $157.76   6.336%   $167.7557   $167.76   $167.75   $167.80  
  Purchase #3 $40.60   7.704%   $43.7278   $43.73   $43.75   $43.70  
  Purchase #4 $120.43   8.539%   $130.7135   $130.71   $130.70   $130.70  
  Purchase #5 $194.67   4.750%   $203.9168   $203.92   $203.90   $203.90  
  Purchase #6 $156.69   6.328%   $166.6053   $166.61   $166.60   $166.60  
  Purchase #7 $15.85   7.630%   $17.0594   $17.06   $17.05   $17.10  
  7 purchase totals = $934.52       $1,006.0681   $1,006.08   $1,006.05   $1,006.10