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 $76.37   10.767%   $84.5928   $84.59   $84.60   $84.60  
  Purchase #2 $24.89   6.539%   $26.5176   $26.52   $26.50   $26.50  
  Purchase #3 $127.33   9.686%   $139.6632   $139.66   $139.65   $139.70  
  Purchase #4 $136.48   10.813%   $151.2376   $151.24   $151.25   $151.20  
  Purchase #5 $170.92   3.369%   $176.6783   $176.68   $176.70   $176.70  
  Purchase #6 $203.89   7.852%   $219.8994   $219.90   $219.90   $219.90  
  Purchase #7 $59.89   6.634%   $63.8631   $63.86   $63.85   $63.90  
  7 purchase totals = $799.77       $862.4520   $862.45   $862.45   $862.50