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 $25.41   5.579%   $26.8276   $26.83   $26.85   $26.80  
  Purchase #2 $158.71   13.205%   $179.6677   $179.67   $179.65   $179.70  
  Purchase #3 $166.61   5.358%   $175.537   $175.54   $175.55   $175.50  
  Purchase #4 $216.79   7.424%   $232.8845   $232.88   $232.90   $232.90  
  Purchase #5 $241.59   13.496%   $274.195   $274.20   $274.20   $274.20  
  Purchase #6 $99.87   11.226%   $111.0814   $111.08   $111.10   $111.10  
  Purchase #7 $208.83   8.804%   $227.2154   $227.22   $227.20   $227.20  
  7 purchase totals = $1,117.81       $1,227.4086   $1,227.42   $1,227.45   $1,227.40