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 $159.95   10.123%   $176.1417   $176.14   $176.15   $176.10  
  Purchase #2 $177.56   9.582%   $194.5738   $194.57   $194.55   $194.60  
  Purchase #3 $249.76   9.702%   $273.9917   $273.99   $274.00   $274.00  
  Purchase #4 $61.91   9.823%   $67.9914   $67.99   $68.00   $68.00  
  Purchase #5 $107.59   5.564%   $113.5763   $113.58   $113.60   $113.60  
  Purchase #6 $103.85   11.446%   $115.7367   $115.74   $115.75   $115.70  
  Purchase #7 $212.37   11.103%   $235.9494   $235.95   $235.95   $235.90  
  7 purchase totals = $1,072.99       $1,177.9610   $1,177.96   $1,178.00   $1,177.90