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 $244.62   11.660%   $273.1427   $273.14   $273.15   $273.10  
  Purchase #2 $70.30   5.534%   $74.1904   $74.19   $74.20   $74.20  
  Purchase #3 $152.67   12.192%   $171.2835   $171.28   $171.30   $171.30  
  Purchase #4 $156.88   3.630%   $162.5747   $162.57   $162.55   $162.60  
  Purchase #5 $46.55   5.219%   $48.9794   $48.98   $49.00   $49.00  
  Purchase #6 $50.91   9.273%   $55.6309   $55.63   $55.65   $55.60  
  Purchase #7 $232.91   6.584%   $248.2448   $248.24   $248.25   $248.20  
  7 purchase totals = $954.84       $1,034.0464   $1,034.03   $1,034.10   $1,034.00