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 $209.69   10.722%   $232.173   $232.17   $232.15   $232.20  
  Purchase #2 $188.50   12.307%   $211.6987   $211.70   $211.70   $211.70  
  Purchase #3 $51.26   11.158%   $56.9796   $56.98   $57.00   $57.00  
  Purchase #4 $67.85   12.760%   $76.5077   $76.51   $76.50   $76.50  
  Purchase #5 $211.45   7.826%   $227.9981   $228.00   $228.00   $228.00  
  Purchase #6 $239.59   13.234%   $271.2973   $271.30   $271.30   $271.30  
  Purchase #7 $165.61   6.389%   $176.1908   $176.19   $176.20   $176.20  
  7 purchase totals = $1,133.95       $1,252.8452   $1,252.85   $1,252.85   $1,252.90