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 $24.40   8.705%   $26.524   $26.52   $26.50   $26.50  
  Purchase #2 $48.29   11.619%   $53.9008   $53.90   $53.90   $53.90  
  Purchase #3 $232.93   7.267%   $249.857   $249.86   $249.85   $249.90  
  Purchase #4 $76.96   9.238%   $84.0696   $84.07   $84.05   $84.10  
  Purchase #5 $219.83   6.594%   $234.3256   $234.33   $234.35   $234.30  
  Purchase #6 $90.65   8.586%   $98.4332   $98.43   $98.45   $98.40  
  Purchase #7 $9.59   10.262%   $10.5741   $10.57   $10.55   $10.60  
  7 purchase totals = $702.65       $757.6843   $757.68   $757.65   $757.70