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 $88.51   11.285%   $98.4984   $98.50   $98.50   $98.50  
  Purchase #2 $23.54   12.526%   $26.4886   $26.49   $26.50   $26.50  
  Purchase #3 $67.38   4.749%   $70.5799   $70.58   $70.60   $70.60  
  Purchase #4 $112.86   5.418%   $118.9748   $118.97   $118.95   $119.00  
  Purchase #5 $11.84   11.326%   $13.181   $13.18   $13.20   $13.20  
  Purchase #6 $206.96   12.268%   $232.3499   $232.35   $232.35   $232.30  
  Purchase #7 $212.52   3.181%   $219.2803   $219.28   $219.30   $219.30  
  7 purchase totals = $723.61       $779.3529   $779.35   $779.40   $779.40