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 $90.58   5.528%   $95.5873   $95.59   $95.60   $95.60  
  Purchase #2 $10.86   3.156%   $11.2027   $11.20   $11.20   $11.20  
  Purchase #3 $138.28   13.183%   $156.5095   $156.51   $156.50   $156.50  
  Purchase #4 $224.59   10.735%   $248.6997   $248.70   $248.70   $248.70  
  Purchase #5 $152.31   6.578%   $162.329   $162.33   $162.35   $162.30  
  Purchase #6 $76.60   13.570%   $86.9946   $86.99   $87.00   $87.00  
  Purchase #7 $59.68   13.848%   $67.9445   $67.94   $67.95   $67.90  
  7 purchase totals = $752.90       $829.2673   $829.26   $829.30   $829.20