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 $216.68   13.753%   $246.48   $246.48   $246.50   $246.50  
  Purchase #2 $132.70   4.432%   $138.5813   $138.58   $138.60   $138.60  
  Purchase #3 $95.78   10.187%   $105.5371   $105.54   $105.55   $105.50  
  Purchase #4 $168.46   11.154%   $187.25   $187.25   $187.25   $187.30  
  Purchase #5 $79.35   8.796%   $86.3296   $86.33   $86.35   $86.30  
  Purchase #6 $178.45   11.341%   $198.688   $198.69   $198.70   $198.70  
  Purchase #7 $183.44   5.559%   $193.6374   $193.64   $193.65   $193.60  
  7 purchase totals = $1,054.86       $1,156.5034   $1,156.51   $1,156.60   $1,156.50