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 $207.26   13.190%   $234.5976   $234.60   $234.60   $234.60  
  Purchase #2 $24.44   10.109%   $26.9106   $26.91   $26.90   $26.90  
  Purchase #3 $124.71   7.760%   $134.3875   $134.39   $134.40   $134.40  
  Purchase #4 $45.89   4.320%   $47.8724   $47.87   $47.85   $47.90  
  Purchase #5 $174.95   8.612%   $190.0167   $190.02   $190.00   $190.00  
  Purchase #6 $198.92   9.243%   $217.3062   $217.31   $217.30   $217.30  
  Purchase #7 $95.98   7.815%   $103.4808   $103.48   $103.50   $103.50  
  7 purchase totals = $872.15       $954.5718   $954.58   $954.55   $954.60