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 $144.79   5.332%   $152.5102   $152.51   $152.50   $152.50  
  Purchase #2 $26.42   4.582%   $27.6306   $27.63   $27.65   $27.60  
  Purchase #3 $35.92   13.305%   $40.6992   $40.70   $40.70   $40.70  
  Purchase #4 $185.71   5.195%   $195.3576   $195.36   $195.35   $195.40  
  Purchase #5 $111.70   8.594%   $121.2995   $121.30   $121.30   $121.30  
  Purchase #6 $187.72   9.811%   $206.1372   $206.14   $206.15   $206.10  
  Purchase #7 $224.39   12.176%   $251.7117   $251.71   $251.70   $251.70  
  7 purchase totals = $916.65       $995.3460   $995.35   $995.35   $995.30