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 $184.35   6.709%   $196.718   $196.72   $196.70   $196.70  
  Purchase #2 $26.85   11.705%   $29.9928   $29.99   $30.00   $30.00  
  Purchase #3 $152.95   8.303%   $165.6494   $165.65   $165.65   $165.60  
  Purchase #4 $65.56   5.643%   $69.2596   $69.26   $69.25   $69.30  
  Purchase #5 $151.73   13.447%   $172.1331   $172.13   $172.15   $172.10  
  Purchase #6 $240.73   13.778%   $273.8978   $273.90   $273.90   $273.90  
  Purchase #7 $243.91   6.186%   $258.9983   $259.00   $259.00   $259.00  
  7 purchase totals = $1,066.08       $1,166.6490   $1,166.65   $1,166.65   $1,166.60