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 $184.67   12.771%   $208.2542   $208.25   $208.25   $208.30  
  Purchase #2 $65.99   12.576%   $74.2889   $74.29   $74.30   $74.30  
  Purchase #3 $185.48   4.260%   $193.3814   $193.38   $193.40   $193.40  
  Purchase #4 $83.90   8.539%   $91.0642   $91.06   $91.05   $91.10  
  Purchase #5 $165.30   8.323%   $179.0579   $179.06   $179.05   $179.10  
  Purchase #6 $41.70   7.871%   $44.9822   $44.98   $45.00   $45.00  
  Purchase #7 $232.72   11.585%   $259.6806   $259.68   $259.70   $259.70  
  7 purchase totals = $959.76       $1,050.7094   $1,050.70   $1,050.75   $1,050.90