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 $38.84   11.869%   $43.4499   $43.45   $43.45   $43.40  
  Purchase #2 $201.55   10.146%   $221.9993   $222.00   $222.00   $222.00  
  Purchase #3 $242.46   10.129%   $267.0188   $267.02   $267.00   $267.00  
  Purchase #4 $172.86   8.176%   $186.993   $186.99   $187.00   $187.00  
  Purchase #5 $157.49   12.188%   $176.6849   $176.68   $176.70   $176.70  
  Purchase #6 $239.84   8.734%   $260.7876   $260.79   $260.80   $260.80  
  Purchase #7 $225.65   5.170%   $237.3161   $237.32   $237.30   $237.30  
  7 purchase totals = $1,278.69       $1,394.2496   $1,394.25   $1,394.25   $1,394.20