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 $243.95   13.546%   $276.9955   $277.00   $277.00   $277.00  
  Purchase #2 $35.54   5.868%   $37.6255   $37.63   $37.65   $37.60  
  Purchase #3 $133.72   13.687%   $152.0223   $152.02   $152.00   $152.00  
  Purchase #4 $222.59   13.827%   $253.3675   $253.37   $253.35   $253.40  
  Purchase #5 $198.49   7.699%   $213.7717   $213.77   $213.75   $213.80  
  Purchase #6 $214.90   4.539%   $224.6543   $224.65   $224.65   $224.70  
  Purchase #7 $85.26   9.133%   $93.0468   $93.05   $93.05   $93.00  
  7 purchase totals = $1,134.45       $1,251.4836   $1,251.49   $1,251.45   $1,251.50