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 $227.80   11.772%   $254.6166   $254.62   $254.60   $254.60  
  Purchase #2 $227.65   9.830%   $250.028   $250.03   $250.05   $250.00  
  Purchase #3 $95.53   12.304%   $107.284   $107.28   $107.30   $107.30  
  Purchase #4 $44.63   7.449%   $47.9545   $47.95   $47.95   $48.00  
  Purchase #5 $35.55   8.547%   $38.5885   $38.59   $38.60   $38.60  
  Purchase #6 $222.62   3.451%   $230.3026   $230.30   $230.30   $230.30  
  Purchase #7 $155.67   3.394%   $160.9534   $160.95   $160.95   $161.00  
  7 purchase totals = $1,009.45       $1,089.7276   $1,089.72   $1,089.75   $1,089.80