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 $211.53   10.306%   $233.3303   $233.33   $233.35   $233.30  
  Purchase #2 $73.53   5.682%   $77.708   $77.71   $77.70   $77.70  
  Purchase #3 $175.39   5.823%   $185.603   $185.60   $185.60   $185.60  
  Purchase #4 $58.83   10.340%   $64.913   $64.91   $64.90   $64.90  
  Purchase #5 $187.53   6.692%   $200.0795   $200.08   $200.10   $200.10  
  Purchase #6 $22.93   13.591%   $26.0464   $26.05   $26.05   $26.00  
  Purchase #7 $85.95   7.694%   $92.563   $92.56   $92.55   $92.60  
  7 purchase totals = $815.69       $880.2432   $880.24   $880.25   $880.20